Organic Semiconductor Material and Light-Emitting Element, Light-Emitting Device, Lighting System, and Electronic Device Using the Same

ABSTRACT

Disclosed is a novel organic semiconductor material which has a twisted quaterphenylene skeleton as a central unit and simultaneously possesses a skeleton having an electron-transporting property and a skeleton having a hole-transporting property at the terminals of the quaterphenylene skeleton. Specifically, the organic semiconductor material has a [1,1′:2′,1″:2″,1′″]quaterphenyl-4-4′″-diyl group, and one of the terminals of the [1,1′:2′,1″:2″,1′″]quaterphenyl-4-4′″-diyl group is bonded to a skeleton having an electron-transporting property such as a benzoxazole group or an oxadiazole group. A skeleton having a hole-transporting property such as diarylamino group is introduced at the other terminal. This structure allows the formation of a compound having a bipolar property, a high molecular weight, an excellent thermal stability, a large band gap, and high triplet excitation energy.

TECHNICAL FIELD

The present invention relates to an organic semiconductor. The presentinvention also relates to a light-emitting element, a light-emittingdevice, a lighting system, and an electronic device in each of which anyof the above materials is used.

BACKGROUND ART

An organic compound can take various structures in comparison with aninorganic compound, and it is possible to synthesize a material havingvarious functions by appropriate molecular design of an organiccompound. Owing to those advantages, electronics utilizing a functionalorganic material has been attracting attention in recent years.

For example, a solar cell, a light-emitting element, an organictransistor, and the like are given as examples of an electronic deviceutilizing an organic compound as a functional material. Those aredevices taking advantage of electric properties and optical propertiesof the organic compound. Among them, in particular, a light-emittingelement has been remarkably developed.

It is said that the light emission mechanism of a light-emitting elementis as follows: by application of voltage between a pair of electrodeswith a light-emitting layer interposed therebetween, electrons injectedfrom a cathode and holes injected from an anode are recombined in thelight-emitting layer to form molecular excitons and when the molecularexcitons relax to a ground state, energy is released to emit light.Singlet excitation (S*) and triplet excitation (T*) are known as excitedstates. Light emission is considered possible through either singletexcitation or triplet excitation. Further, the statistical generationratio thereof in a light-emitting element is considered to be S*:T*=1:3.

As for a compound in which a singlet excited state is converted to lightemission (hereinafter, such a compound is referred to as a “fluorescentcompound”), light emission from a triplet excited state(phosphorescence) is not observed but only light emission from a singletexcited state (fluorescence) is observed at a room temperature.Accordingly, the internal quantum efficiency (the ratio of generatedphotons to injected carriers) in a light-emitting element using afluorescent compound is assumed to have a theoretical limit of 25% basedon the relationship of S*:T*=1:3.

On the other hand, when a compound in which a triplet excited state isconverted into light emission (hereinafter, such a compound is referredto as a “phosphorescent compound”) is used, internal quantum efficiencycan be theoretically 75% to 100%. In other words, emission efficiencythat is 3 times to 4 times as much as that of the fluorescence compoundcan be achieved. For those reasons, in order to achieve a highlyefficient light-emitting element, a light-emitting element in which aphosphorescent compound is used has been actively developed recently.

When a light-emitting layer of a light-emitting element is formed usingthe above phosphorescent compound, in order to suppress concentrationquenching of the phosphorescent compound or quenching due totriplet-triplet annihilation (T-T annihilation), the light-emittinglayer is often formed so that the phosphorescent compound is dispersedin a matrix of another substance. In the above case, the substance,which serves as a matrix, is referred to as a host material, and thesubstance, like a phosphorescent substance, which is dispersed in amatrix, is referred to as a guest material.

In the case where a phosphorescent compound is used as a guest material,a host material is required to have a large energy gap (a differencebetween the highest occupied molecular orbital level (HOMO level) andthe lowest unoccupied molecular orbital level (LUMO level)) or highertriplet excitation energy (a difference in energy between a ground stateand a triplet excited state) than that of the phosphorescent compound.Therefore, a substance having such characteristics has been developed.

For example, in Non Patent Document 1, a material which has aquaterphenylene skeleton is used as a host material of a phosphorescentcompound which exhibits blue light emission and as a hole-transportinglayer.

-   [Non Patent Document 1]-   J. Kido et. al., Chemistry Letters, Vol. 36, No. 2, 316-317 (2007)

DISCLOSURE OF INVENTION

As is clear from the fact that the host material described in Non PatentDocument 1 is used for the hole-transporting layer, the host materialexhibits a hole-transporting property. Therefore, it is expected thatholes penetrate a light-emitting layer in the case where the materialdescribed in Non Patent Document 1 is used as a host material of thelight-emitting layer. In Non Patent Document 1, it is considered that anelectron-transporting layer is formed using t-BuTAZ which is ahole-blocking material on the cathode side of the light-emitting layerin order that holes are prevented from penetrating the light-emittinglayer. As described above, since the host material of the light-emittinglayer has a hole-transporting property, a light-emitting region couldexist close to an interface between the light-emitting layer and theelectron-transporting layer (a hole-blocking layer).

When the light-emitting region locally exists, quenching due totriplet-triplet annihilation (T-T annihilation) or dispersion ofexcitons into a layer adjacent to the light-emitting layer (thehole-transporting layer, the electron-transporting layer, or thehole-blocking layer) arises, which results in decrease of luminousefficiency.

Thus, the host material is required to have a bipolar property whichenables oxidation and reduction and to be stable against repetitiveoxidation and reduction cycles. However, when a skeleton having anelectron-transporting property and a skeleton having a hole-transportingproperty are directly bonded, decrease in a band gap is caused, whichmakes it difficult to synthesize a material having high tripletexcitation energy. In addition, when a substituent is introduced betweenthe skeleton having an electron-transporting property and the skeletonhaving a hole-transporting property to expand a conjugation system,problems such as decrease in a band gap and triplet excitation energyoccur.

In view of the above problems, it is an object of an embodiment of thepresent invention to provide a novel material having a bipolar property.

It is another object of the present invention to reduce driving voltageof a light-emitting element. It is still another object to improveemission efficiency of a light-emitting element.

It is yet another object to reduce power consumption of a light-emittingelement, a light-emitting device, and an electronic device.

The present inventors have found out that a material, in which askeleton having an electron-transporting property and a skeleton havinga hole-transporting property are bonded through a twistedquaterphenylene skeleton that inhibits extension of conjugation, has alarge energy gap and an electron-transporting property and ahole-transporting property (that is, a bipolar property).

Specifically, they have found out that a material represented by GeneralFormula (G1) in which a [1,1′:2′,1″:2″,1′″]quaterphenyl-4-4′″-diyl groupis applied as a quaterphenylene skeleton has a large energy gap and anelectron-transporting property and a hole-transporting property.

In some cases, even if a compound has a skeleton having anelectron-transporting property and a skeleton having a hole-transportingproperty, it does not have a bipolar property. However, an organicsemiconductor material of an embodiment of the present invention has atwisted quaterphenylene skeleton, in which a conjugation hardly extends,in the center; thus, the organic semiconductor material is considered tohave a limited intramolecular interaction between a skeleton having anelectron-transporting property and a skeleton having a hole-transportingproperty, which contributes to realization of a bipolar property.

Thus, an embodiment of the present invention is an organic semiconductormaterial represented by General Formula (G1).

In the formula, E_(A) represents an electron-accepting unit, H_(A)represents a hole-accepting unit; carbon of α1 and E_(A) may be bondedto form a ring; and carbon of α2 and H_(A) may be bonded to form a ring.

In the above structure, the electron affinity and ionization potentialof the electron-accepting unit are greater than those of thehole-accepting unit. Note that the electron-accepting unit is theskeleton having an electron-transporting property, and thehole-accepting unit is the skeleton having a hole-transporting property.

Specifically, an embodiment of the present invention is an organicsemiconductor material represented by General Formula (G1).

In the formula, E_(A) and H_(A) are each a substituent; carbon of α1 andE_(A) may be bonded to form a ring; and carbon of α2 and H_(A) may bebonded to form a ring. In addition, a compound represented by GeneralFormula (G2A) which corresponds to a partial structure a has greaterelectron affinity and ionization potential than a compound representedby General Formula (G2B) which corresponds to a partial structure b.

In the above structure, the electron affinity of the compoundrepresented by General Formula (G2A) is preferably greater than or equalto 2.0 eV and less than or equal to 4.0 eV and the ionization potentialof the compound represented by General Formula (G2B) is preferablygreater than or equal to 4.5 eV and less than or equal to 6.5 eV. Inparticular, in the case of being used for a light-emitting element, theelectron affinity of the compound represented by General Formula (G2A)is preferably greater than or equal to 2.0 eV and less than or equal to3.0 eV and the ionization potential of the compound represented byGeneral Formula (G2B) is preferably greater than or equal to 5.0 eV andless than or equal to 6.0 eV.

In the above structure, as the substituent represented by E_(A), anitrogen-containing 6-membered aromatic ring group, a 1,2-azole group, a1,3-azole group, a polyazole group, and the like are given.

In the above structure, as the substituent represented by H_(A), aπ-electron rich heteroaromatic substituent group, a diarylamino group,and the like are given.

In the organic semiconductor material represented by General Formula(G1), a benzoxazole skeleton can be selected as a skeleton having anelectron-transporting property (E_(A)).

Thus, an embodiment of the present invention is a benzoxazole derivativerepresented by General Formula (BOX 1).

In the formula, Ar¹ and Ar² each independently represent a substitutedor unsubstituted aryl group having 6 to 13 carbon atoms; and R¹ to R⁴each independently represent any of hydrogen, an alkyl group having 1 to4 carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen. Ar¹ and carbon of α, or Ar¹ and Ar² may be bonded directlyor through sulfur, oxygen, or nitrogen.

Further, an embodiment of the present invention is a benzoxazolederivative represented by General Formula (BOX2).

In the formula, R¹ to R⁴ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, an unsubstituted aryl grouphaving 6 to 10 carbon atoms, or halogen; and R¹¹ to R²⁰ eachindependently represent any of hydrogen, alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted aryl group having 6 to13 carbon atoms. A carbon atom of the benzene ring which is bonded toR¹¹ and carbon of α, or a carbon atom of the benzene ring which isbonded to R¹⁵ and a carbon atom of the benzene ring which is bonded toR²⁰ may be directly bonded.

Further, an embodiment of the present invention is a benzoxazolederivative represented by General Formula (BOX2).

In the formula, R¹ to R⁴ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, an unsubstituted aryl grouphaving 6 to 10 carbon atoms, or halogen; and R¹¹ to R²⁰ eachindependently represent any of hydrogen, alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted aryl group having 6 to13 carbon atoms. A carbon atom of the benzene ring which is bonded toR¹¹ and carbon of α, or a carbon atom of the benzene ring which isbonded to R¹⁵ and a carbon atom of the benzene ring which is bonded toR²⁰ may be directly bonded to form a carbazole skeleton.

Further, an embodiment of the present invention is a benzoxazolederivative represented by General Formula (BOX3).

In the formula, R¹¹ to R²⁰ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. A carbon atom ofthe benzene ring which is bonded to R¹¹ and carbon of α, or a carbonatom of the benzene ring which is bonded to R¹⁵ and a carbon atom of thebenzene ring which is bonded to R²⁰ may be directly bonded to form acarbazole skeleton.

Further, in the organic semiconductor material represented by GeneralFormula (G1), an oxadiazole skeleton can be selected as a skeletonhaving an electron-transporting property (E_(A)).

Thus, an embodiment of the present invention is an oxadiazole derivativerepresented by General Formula (OXD1).

In the formula, Ar¹¹, Ar¹², and Ar¹³ each represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. In addition, Ar¹¹and carbon of α, or Ar¹¹ and Ar¹² may be bonded directly or through anyof oxygen, sulfur, or nitrogen.

The oxadiazole derivative represented by General Formula (OXD1) ispreferably an oxadiazole derivative represented by General Formula(OXD2).

In the formula, R³¹ to R⁴⁰ each represent any of hydrogen, an alkylgroup having 1 to 4 carbon atoms, or an unsubstituted aryl group having6 to 13 carbon atoms; and Ar¹³ represents a substituted or unsubstitutedaryl group having 6 to 13 carbon atoms. In addition, a carbon atom ofthe benzene ring which is bonded to R³¹ and carbon of a, or a carbonatom of the benzene ring which is bonded to R³⁵ and a carbon atom of thebenzene ring which is bonded to R⁴⁰ may be directly bonded to form acarbazole skeleton.

Further, in the oxadiazole derivative represented by General Formula(OXD2), Ar¹³ preferably represents any of a substituted or unsubstitutedphenyl group or a substituted or unsubstituted naphthyl group, and Ar¹³more preferably represents any of an unsubstituted phenyl group, anunsubstituted 1-naphthyl group, or an unsubstituted 2-naphthyl group.

Since the above organic semiconductor material has a bipolar property,it can be favorably used for a light-emitting element or an organicdevice such as an organic transistor.

Thus, an embodiment of the present invention is a light-emitting elementin which the above organic semiconductor material is used.

In particular, since the above organic semiconductor material has hightriplet excitation energy, it has more prominent effect in the case ofbeing used for a light-emitting element together with a phosphorescentcompound.

Thus, an embodiment of the present invention is a light-emitting elementin which the above organic semiconductor material is included between apair of electrodes and a phosphorescent compound is included in alight-emitting layer.

Further, the above organic semiconductor material has a bipolarproperty, and thus is preferably used for a light-emitting layer.

Moreover, an embodiment of the present invention also includes, in itscategory, a light-emitting device having the above light-emittingelement.

Note that the light-emitting device in this specification includes, inits category, an image display device, a light-emitting device, and alight source (including a lighting system). Further, the following areall included in the category of the light-emitting device: a module inwhich a connector, for example, a flexible printed circuit (FPC), a tapeautomated bonding (TAB) tape, or a tape carrier package (TCP) isattached to a panel provided with a light-emitting element; a moduleprovided with a printed wiring board at the end of the TAB tape or theTCP; and a module in which an IC (integrated circuit) is directlymounted to a light-emitting element by a chip on glass (COG) method.

Further, an embodiment of the present invention also includes, in itscategory, an electronic device in which the above light-emitting elementis used for a display portion. Therefore, the electronic device of anembodiment of the present invention has a display portion in which theabove light-emitting element is used.

Effect of the Invention

The organic semiconductor material of an embodiment of the presentinvention is a novel bipolar material.

In addition, the benzoxazole derivative of an embodiment of the presentinvention is a novel bipolar material.

Moreover, the oxadiazole derivative of an embodiment of the presentinvention is a novel bipolar material.

Further, application of an embodiment of the present invention makes itpossible to reduce driving voltage of a light-emitting element. Inaddition, emission efficiency of a light-emitting element can beimproved.

Further, application of an embodiment of the present invention makes itpossible to reduce power consumption of a light-emitting element, alight-emitting device, and an electronic device.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a light-emitting element of an embodiment of thepresent invention;

FIG. 2 illustrates a light-emitting element of an embodiment of thepresent invention;

FIG. 3 illustrates a light-emitting element of an embodiment of thepresent invention;

FIGS. 4A and 4B illustrate a light-emitting device of an embodiment ofthe present invention;

FIGS. 5A and 5B illustrate a light-emitting device of an embodiment ofthe present invention;

FIGS. 6A to 6E each illustrate an electronic device of an embodiment ofthe present invention;

FIG. 7 illustrates an electronic device of an embodiment of the presentinvention;

FIG. 8 illustrates an electronic device of an embodiment of the presentinvention;

FIG. 9 illustrates an electronic device of an embodiment of the presentinvention;

FIG. 10 illustrates a lighting device of an embodiment of the presentinvention;

FIG. 11 illustrates a lighting device of an embodiment of the presentinvention;

FIGS. 12A to 12C illustrate an electronic device of an embodiment of thepresent invention;

FIG. 13 shows CV measurement results of 2,5-diphenyl-1,3,4-oxadiazole;

FIG. 14 shows CV measurement results of 2,5-diphenyl-1,3,4-oxadiazole;

FIG. 15 shows CV measurement results of 2-phenylbenzoxazole;

FIG. 16 shows CV measurement results of 2-phenylbenzoxazole;

FIG. 17 shows CV measurement results of 9-phenyl-9H-carbazole;

FIG. 18 shows CV measurement results of 9-phenyl-9H-carbazole;

FIG. 19 shows CV measurement results of triphenylamine;

FIG. 20 shows CV measurement results of triphenylamine;

FIG. 21 shows CV measurement results of Z-CzPO11;

FIG. 22 shows CV measurement results of Z-CzPO11;

FIGS. 23A and 23B each show an absorption spectrum and an emissionspectrum of Z-CzPO11;

FIG. 24 shows CV measurement results of Z-DPhAO11;

FIG. 25 shows CV measurement results of Z-DPhAO11;

FIGS. 26A and 26B each show an absorption spectrum and an emissionspectrum of Z-DPhAO11;

FIG. 27 shows CV measurement results of Z-CzPBOx;

FIG. 28 shows CV measurement results of Z-CzPBOx;

FIGS. 29A and 29B each illustrate an absorption spectrum and an emissionspectrum of Z-CzPBOx;

FIG. 30 shows CV measurement results of Z-DPhABOx;

FIG. 31 shows CV measurement results of Z-DPhABOx;

FIGS. 32A and 32B each show an absorption spectrum and an emissionspectrum of Z-DPhABOx;

FIG. 33 illustrates a light-emitting element in Examples;

FIG. 34 shows current density-luminance characteristics oflight-emitting elements manufactured in Example 3;

FIG. 35 shows voltage-luminance characteristics of light-emittingelements manufactured in Example 3;

FIG. 36 shows luminance-current efficiency characteristics of thelight-emitting elements manufactured in Example 3;

FIG. 37 shows emission spectra of the light-emitting elementsmanufactured in Example 3;

FIG. 38 shows current density-luminance characteristics of alight-emitting element manufactured in Example 4;

FIG. 39 shows voltage-luminance characteristics of the light-emittingelement manufactured in Example 4;

FIG. 40 shows luminance-current efficiency characteristics of thelight-emitting element manufactured in Example 4;

FIG. 41 shows an emission spectrum of the light-emitting elementmanufactured in Example 4;

FIG. 42 shows current density-luminance characteristics oflight-emitting elements manufactured in Example 5;

FIG. 43 shows voltage-luminance characteristics of the light-emittingelements manufactured in Example 5;

FIG. 44 shows luminance-current efficiency characteristics of thelight-emitting elements manufactured in Example 5;

FIG. 45 shows emission spectra of the light-emitting elementsmanufactured in Example 5;

FIG. 46 shows current density-luminance characteristics of alight-emitting element manufactured in Example 6;

FIG. 47 shows voltage-luminance characteristics of the light-emittingelement manufactured in Example 6;

FIG. 48 shows luminance-current efficiency characteristics of thelight-emitting element manufactured in Example 6;

FIG. 49 shows an emission spectrum of the light-emitting elementmanufactured in Example 6;

FIGS. 50A and 50B show ¹H NMR charts of Z-CzPO11;

FIGS. 51A and 51B show ¹H NMR charts of Z-DPhPA11;

FIGS. 52A and 52B show ¹H NMR charts of Z-CzPBOx; and

FIGS. 53A and 53B show ¹H NMR charts of Z-DPhABOx.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, Embodiments and Examples of the present invention will bedescribed with reference to the accompanying drawings. Note that it iseasily understood by those skilled in the art that the present inventioncan be carried out in many different modes, and the modes and detailsdisclosed herein can be modified in various ways without departing fromthe spirit and scope of the present invention. Therefore, the presentinvention should not be construed as being limited to the descriptionbelow of the embodiments and examples.

Embodiment 1

In Embodiment 1, an organic semiconductor material of an embodiment ofthe present invention will be described.

An organic semiconductor material of Embodiment 1 has a Zquaterphenylene skeleton ([1,1′:2′,1″:2″,1′″]quaterphenyl-4-4′″-diylgroup). An electron-accepting unit is bonded to a para position of aterminal benzene ring of the Z quaterphenylene skeleton, and ahole-accepting unit is bonded to a para position of the other terminalbenzene ring.

Specifically, the organic semiconductor material of Embodiment 1 is anorganic semiconductor material represented by General Formula (G1).

In the formula, E_(A) represents an electron-accepting unit, H_(A)represents a hole-accepting unit, carbon of α1 and E_(A) may be bondedto form a ring, and carbon of α2 and H_(A) may be bonded to form a ring.

An organic semiconductor material having such a structure has anelectron-accepting unit and a hole-accepting unit in its molecule, andthus is a bipolar material which can transport both electrons and holes.

In some cases, even if a compound has a skeleton having anelectron-accepting unit and a hole-accepting unit in its molecule, itdoes not have a bipolar property. However, the organic semiconductormaterial of Embodiment 1 has two ortho-linked benzene rings in thecenter; thus, the organic semiconductor material is considered to have alimited intramolecular interaction between the electron-accepting unitand the hole-accepting unit, which contributes to realization of abipolar property.

Specifically, in General Formula (G1) shown below, a benzene ring 2 anda benzene ring 3 are bonded at their ortho positions. Those two benzenerings bonded at the ortho positions are considered to limit interactionbetween the substituents bonded to the terminal benzene rings. Thus, anorganic semiconductor material having a bipolar property can beobtained.

Further, the organic semiconductor material represented by GeneralFormula (G1) below is considered to have a twisted structure due to thetwo ortho-linked benzene rings, which suppresses the extension ofconjugation. Thus, the organic semiconductor material can have a largeenergy gap while having a high molecular weight. Accordingly, theorganic semiconductor material can be favorably used as a host materialin a light-emitting layer of a light-emitting element. In addition, theorganic semiconductor material has high triplet excitation energy, andthus can be favorably used for a light-emitting element together with aphosphorescent compound.

Note that increase in the number of the ortho-linked benzene rings makesa synthesis method complicated, which results in decrease in yield. Inaddition, increase in the number of benzene rings increases the distancebetween the electron-accepting unit and the hole-accepting unit.Moreover, since increase in the number of benzene rings increasesproportion of portions other than the units which accept carriers, thehopping distance of carriers is increased, which results in decrease ina carrier-transporting property. Thus, an embodiment of the presentinvention provides, in view of those problems, a bipolar semiconductormaterial with an optimal structure.

Note that the electron-accepting unit has higher electron affinity andionization potential than the hole-accepting unit.

In practice, it is difficult to evaluate the electron affinity and theionization potential of a substituent itself. Therefore, in thespecification, the electron affinity and the ionization potential of theelectron-accepting unit are evaluated using a compound represented byGeneral Formula (G2A) which corresponds to a partial structure a of theorganic semiconductor material represented by General Formula (G1). Inaddition, the electron affinity and the ionization potential of thehole-accepting unit are evaluated using a compound represented byGeneral Formula (G2B) which corresponds to a partial structure b of theorganic semiconductor material represented by General Formula (G1).

In other words, the organic semiconductor material of Embodiment 1 isrepresented by General Formula (G1), and the compound represented byGeneral Formula (G2A) which corresponds to a partial structure a ofGeneral Formula (G1) has higher electron affinity and ionizationpotential than the compound represented by General Formula (G2B) whichcorresponds to a partial structure b of General Formula (G1).

Further, the organic semiconductor material of Embodiment 1 has theortho-linked benzene rings in the center and limited intramolecularinteraction between the electron-accepting unit and the hole-acceptingunit. Therefore, the electron affinity of the organic semiconductormaterial represented by General Formula (G1) and that of the compoundrepresented by General Formula (G2A) are almost the same. Thus, theelectron affinity of the compound represented by General Formula (G2A)is preferably greater than or equal to 2.0 eV and less than or equal to4.0 eV. In particular, in the case where the organic semiconductormaterial represented by General Formula (G1) is used for alight-emitting element, in consideration of the electron affinity of ageneral organic material used for a light-emitting element, the electronaffinity of the compound represented by General Formula (G2A) is morepreferably greater than or equal to 2.0 eV and less than or equal to 3.0eV.

Similarly, the ionization potential of the organic semiconductormaterial represented by General Formula (G1) is almost the same as thatof the ionization potential of the compound represented by GeneralFormula (G2B). Thus, the ionization potential of the compoundrepresented by General Formula (G2B) is preferably greater than or equalto 4.5 eV and less than or equal to 6.5 eV. In particular, in the casewhere the organic semiconductor material represented by General Formula(G1) is used for a light-emitting element, in consideration of theionization potential of a general organic material used for alight-emitting element, the ionization potential of the compoundrepresented by General Formula (G2B) is more preferably greater than orequal to 5.0 eV and less than or equal to 6.0 eV.

The above structure makes it possible to obtain an organic semiconductormaterial having a large band gap.

As the electron-accepting unit E_(A), a π-electron deficientheteroaromatic substituent is preferable so that the electron-acceptingunit E_(A) has high electron affinity. As the π-electron deficientheteroaromatic substituent, the following can be given: anitrogen-containing 6-membered aromatic ring group (note that thenitrogen-containing 6-membered aromatic ring includes a condensedaromatic hydrocarbon and a nitrogen-containing 6-membered condensedaromatic ring), a 1,2-azole group (note that the 1,2-azole includes acondensed aromatic hydrocarbon and a nitrogen-containing 6-memberedcondensed aromatic ring), a 1,3-azole group (note that the 1,3-azoleincludes a condensed aromatic hydrocarbon and a nitrogen-containing6-membered condensed aromatic ring), a polyazole group (note that thepolyazole includes a condensed aromatic hydrocarbon and anitrogen-containing 6-membered condensed aromatic ring), and the like.In particular, the nitrogen-containing 6-membered aromatic ring group,the 1,3-azole group, and the polyazole group are preferable because theyare stable against repetitive reduction-oxidation processes and exhibitsa high electron-transporting property as well as having relatively highelectron affinity.

As the nitrogen-containing 6-membered aromatic ring, the following canbe given for example: a substituted or unsubstituted pyridyl group, asubstituted or unsubstituted pyrazinyl group, a substituted orunsubstituted pyrimidinyl group, a substituted or unsubstitutedpyridazinyl group, a substituted or unsubstituted 1,2,4-triazinyl group,a substituted or unsubstituted 1,3,5-triazinyl group, a substituted orunsubstituted quinolyl group, a substituted or unsubstituted isoquinolylgroup, a substituted or unsubstituted 1,5-naphthyridinyl group, asubstituted or unsubstituted 1,6-naphthyridinyl group, a substituted orunsubstituted 1,7-naphthyridinyl group, a substituted or unsubstituted1,8-naphthyridinyl group, a substituted or unsubstituted2,6-naphthyridinyl group, a substituted or unsubstituted2,7-naphthyridinyl group, a substituted or unsubstituted quinoxalinylgroup, a substituted or unsubstituted quinazolinyl group, a substitutedor unsubstituted phthalazinyl group, a substituted or unsubstitutedcinnolinyl group, a substituted or unsubstituted phenanthridinyl group,a substituted or unsubstituted 1,10-phenanthrolinyl group, and the like.

Further, as the 1,2-azole group, the following can be given, forexample: a substituted or unsubstituted pyrazolyl group, a substitutedor unsubstituted isoxazolyl group, a substituted or unsubstitutedisothiazolyl group, a substituted or unsubstituted indazolyl group, asubstituted or unsubstituted 1,2-benzoisoxazolyl group, a substituted orunsubstituted 1,2-benzoisothiazolyl group, a substituted orunsubstituted 2,1-benzoisoxazolyl group, a substituted or unsubstituted2,1-benzoisothiazolyl group, and the like.

Further, as the 1,3-azole group, the following can be given, forexample: a substituted or unsubstituted imidazolyl group, a substitutedor unsubstituted oxazolyl group, a substituted or unsubstitutedthiazolyl group, a substituted or unsubstituted 1H-benzoimidazolylgroup, a substituted or unsubstituted benzoxazolyl group, a substitutedor unsubstituted benzothiazolyl group, an imidazo[1,2-a]pyridyl group,and the like.

Further, as the polyazole group, the following can be given, forexample: a substituted or unsubstituted 1H-1,2,3-triazolyl group, asubstituted or unsubstituted 1,2,5-oxadiazolyl group, a substituted orunsubstituted 1,2,5-thiadiazolyl group, a substituted or unsubstituted1H-1,2,4-triazolyl group, a substituted or unsubstituted4H-1,2,4-triazolyl group, a substituted or unsubstituted1,2,4-oxadiazolyl group, a substituted or unsubstituted1,2,4-thiadiazolyl group, a substituted or unsubstituted1,3,4-oxadiazolyl group, a substituted or unsubstituted1,3,4-thiadiazolyl group, a substituted or unsubstituted1H-benzotriazolyl group, a substituted or unsubstituted2H-benzotriazolyl group, a substituted or unsubstituted2,1,3-benzoxadiazolyl group, a substituted or unsubstituted2,1,3-benzothiadiazolyl group, and the like.

Note that in the case where the above nitrogen-containing 6-memberedaromatic ring group, 1,2-azole group, 1,3-azole group, and polyazolegroup each have another substituent, the following can be given as thesubstituent: an aryl group such as a phenyl group, a tolyl group, or anaphthyl group; a heteroaromatic group such as a pyridyl group, aquinolyl group, or an isoquinolyl group; an alkyl group such as a methylgroup, an ethyl group, an isopropyl group, a tert-butyl group; and thelike.

The above electron-accepting unit E_(A) is selected as appropriate,whereby the partial structure represented by a can be formed.

As specific examples of the partial structure a in the case where thenitrogen-containing 6-membered aromatic ring group (note that thenitrogen-containing 6-membered aromatic ring includes a condensedaromatic hydrocarbon and a nitrogen-containing 6-membered condensedaromatic ring) is applied as the electron-accepting unit E_(A), thefollowing can be given: a 4-(2-pyridyl)phenyl group, a4-(5-methyl-2-pyridyl)phenyl group, a 4-(6-methyl-2-pyridyl)phenylgroup, a 4-(3-phenyl-2-pyridyl)phenyl group, a4-(6-phenyl-2-pyridyl)phenyl group, a 4-(3-pyridyl)phenyl group, a4-(6-methyl-3-pyridyl)phenyl group, a4-(2,2′:6′,2″-terpyridin-4′-yl)phenyl group, a4-(3-phenylpyrazin-2-yl)phenyl group, a4-(3,5,6-triphenylpyrazin-2-yl)phenyl group, a 4-(pyrimidin-4-yl)phenylgroup, a 4-(6-methylpyrimidin-4-yl)phenyl group, a4-(6-phenylpyrimidin-4-yl)phenyl group, a 4-(pyrimidin-5-yl)phenylgroup, 4-(2,4,6-triphenylpyrimidin-5-yl)phenyl group, a4-(6-phenylpyridazin-3-yl)phenyl group, a4-(3-methyl-1,2,4-triazin-6-yl)phenyl group, a4-(4,6-diphenyl-1,3,5-triazin-2-yl)phenyl group, a 4-(3-quinolyl)phenylgroup, a 4-(8-quinolyl)phenyl group, a 4-(2,4-dimethyl-8-quinolyl)phenylgroup, a 4-(4-isoquinolyl)phenyl group, a4-(1,5-naphthyridin-3-yl)phenyl group, a 4-(1,6-naphthyridin-4-yl)phenylgroup, a 4-(5,7-dimethyl-1,6-naphthyridin-4-yl)phenyl group, a4-(5-methyl-1,6-naphthyridin-2-yl)phenyl group, a4-(1,7-naphthyridin-8-yl)phenyl group, a 4-(1,8-naphthyridin-2-yl)phenylgroup, a 4-(3-methyl-1,8-naphthyridin-2-yl)phenyl group, a4-(1,8-naphthyridin-3-yl)phenyl group, a4-(2-methyl-1,8-naphthyridin-3-yl)phenyl group,4-(1,8-naphthyridin-4-yl)phenyl group, a 4-(2,6-naphthyridin-1-yl)phenylgroup, 4-(2,7-naphthyridin-3-yl)phenyl group, a4-(quinoxalin-2-yl)phenyl group, 4-(3-methylquinoxalin-2-yl)phenylgroup, a 4-(3-isopropylquinoxalin-2-yl)phenyl group, a4-(3-phenylquinoxalin-2-yl)phenyl group, a 4-(quinazolin-4-yl)phenylgroup, a 4-(phthalazin-1-yl)phenyl group,4-(3-phenylcinnolin-4-yl)phenyl group, 4-(phenanthridin-6-yl)phenylgroup, 4-(1,10-phenanthrolin-2-yl)phenyl group,4-(1,10-phenanthrolin-3-yl)phenyl group, and the like.

Further, as specific examples of the partial structure a in the casewhere the 1,2-azole group (note that the 1,2-azole includes a condensedaromatic hydrocarbon and a nitrogen-containing 6-membered condensedaromatic ring) is applied as the electron-accepting unit E_(A), thefollowing can be given: a 4-(3,5-diphenyl-1H-pyrazol-1-yl)phenyl group,a 4-(1,5-diphenyl-1H-pyrazol-3-yl)phenyl group, a4-(5-phenylisoxazol-3-yl)phenyl group, a4-(5-phenylisothiazol-3-yl)phenyl group, a4-(3-methyl-1,2-benzoisoxazol-5-yl)phenyl group, a4-(3-methyl-1,2-benzoisothiazol-5-yl)phenyl group, a4-(2,1-benzoisoxazol-3-yl)phenyl group, a4-(2,1-benzoisothiazol-3-yl)phenyl group, and the like.

Further, as specific examples of the partial structure a in the casewhere the 1,3-azole group (note that the 1,3-azole includes a condensedaromatic hydrocarbon and a nitrogen-containing 6-membered condensedaromatic ring) is applied as the electron-accepting unit E_(A), thefollowing can be given: a 4-(2,4-diphenyl-1H-imidazol-1-yl)phenyl group,a 4-(2-phenyloxazol-4-yl)phenyl group, a 4-(2-phenylthiazol-4-yl)phenylgroup, a 4-(1-methyl-1H-benzoimidazol-2-yl)phenyl group, a4-(1-ethyl-1H-benzoimidazol-2-yl)phenyl group, a4-(1-phenyl-1H-benzoimidazol-2-yl)phenyl group, a4-(2-phenyl-1H-benzoimidazol-1-yl)phenyl group, a4-(benzoxazol-2-yl)phenyl group, a 4-(5-phenylbenzoxazol-2-yl)phenylgroup, a 4-[5-(p-tolyl)benzoxazol-2-yl]phenyl group, a4-(benzothiazol-2-yl)phenyl group, a 4-(5-phenylbenzothiazol-2-yl)phenyl group, a 4-[5-(p-tolyl)benzothiazol-2-yl]phenylgroup, a 4-(imidazo[1,2-a]pyridin-2-yl)phenyl group, a4-(5-phenylimidazo[1,2-a]pyridin-2-yl)phenyl group, and the like.

Further, as specific examples of the partial structure a in the casewhere the polyazole group (note that the polyazole includes a condensedaromatic hydrocarbon and a nitrogen-containing 6-membered condensedaromatic ring) is applied as the electron-accepting unit E_(A), thefollowing can be given: a 4-(1-phenyl-1H-1,2,3-triazol-4-yl)phenylgroup, a 4-(4-phenyl-1,2,5-oxadiazol-3-yl)phenyl group, a4-(4-phenyl-1,2,5-thiadiazol-3-yl)phenyl group, a4-(5-methyl-1-phenyl-1H-1,2,4-triazol-3-yl)phenyl group, a4-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenyl group, a4-[4-(4-sec-butylphenyl)-5-phenyl-4H-1,2,4-triazol-3-yl]phenyl group, a4-(3,5-diphenyl-4H-1,2,4-triazol-4-yl)phenyl group, a4-[4-phenyl-5-(2-pyridyl)-4H-1,2,4-triazol-3-yl]phenyl group, a4-[5-(2-pyridyl)-4-(4-pyridyl)-4H-1,2,4-triazol-3-yl]phenyl group, a4-[5-phenyl-4-(8-quinolyl)-4H-1,2,4-triazol-3-yl]phenyl group, a4-(3-phenyl-1,2,4-oxadiazol-5-yl)phenyl group, a4-(3-phenyl-1,2,4-thiadiazol-5-yl)phenyl group, a4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl group, a4-[5-(4-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]phenyl group, a4-[5-(2-naphthyl)-1,3,4-oxadiazol-2-yl]phenyl group, a4-{5-[4-(1-naphthyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl group, a4-{5-[4-(2-naphthyl)phenyl]-1,3,4-oxadiazol-2-yl}phenyl group, a4-(5-phenyl-1,3,4-thiadiazol-2-yl)phenyl group, a4-[5-(4-tert-butylphenyl)-1,3,4-thiadiazol-2-yl]phenyl group, a4-[5-(2-naphthyl)-1,3,4-thiadiazol-2-yl]phenyl group, a4-{5-[4-(1-naphthyl)phenyl]-1,3,4-thiadiazol-2-yl}phenyl group, a4-{5-[4-(2-naphthyl)phenyl]-1,3,4-thiadiazol-2-yl}phenyl group, and thelike.

Note that in the partial structure a, the electron-accepting unit E_(A)may be bonded to carbon of al to form a ring. A specific example of thatcase is described below. As shown below, when a 3-phenylpyrazin-2-ylgroup is selected as the electron-accepting unit E_(A), the partialstructure a becomes a 4-(3-phenylpyrazin-2-yl)phenyl group (StructuralFormula (11)). In this 4-(3-phenylpyrazin-2-yl)phenyl group (StructuralFormula (11)), when the electron-accepting unit E_(A) and carbon of α1are bonded, the partial structure a becomes adibenzo[f,h]quinoxalin-7-yl group (Structural Formula (12)). Thus, thepartial structure a of Embodiment 1 includes thedibenzo[f,h]quinoxalin-7-yl group. This is just an example, and the samemodification can be applied to the cases where other electron-acceptingunits E_(A) are selected.

As the hole-accepting unit, a π-electron rich heteroaromatic substituentor a diarylamino group is preferable so that the hole-accepting unit hassmall ionization potential. Note that as for the diarylamino group, arylgroups may be directly bonded to form a carbazole ring or they may bebonded through nitrogen, oxygen, or sulfur to form a ring. Inparticular, the diarylamino group (including the case where aryl groupsare directly bonded to form a carbazole ring or they are bonded throughnitrogen, oxygen, or sulfur to form a ring) is preferable because it isstable against repetitive oxidation-reduction cycles and exhibits a highhole-transporting property as well as having relatively small ionizationpotential.

As the π-electron rich heteroaromatic substituent, a monohetero5-membered aromatic ring group (note that the monohetero 5-memberedaromatic ring includes a condensed aromatic hydrocarbon and anitrogen-containing 6-membered condensed aromatic ring) is given.Specifically, the following can be given: a substituted or unsubstitutedpyrrolyl group, a substituted or unsubstituted furyl group, asubstituted or unsubstituted thienyl group, a substituted orunsubstituted indolyl group, a substituted or unsubstituted benzofurylgroup, a substituted or unsubstituted benzothienyl group, a substitutedor unsubstituted isoindolyl group, a substituted or unsubstitutedisobenzofuryl group, a substituted or unsubstituted isobenzothienylgroup, and the like.

Further, as the diarylamino group, the following can be given: asubstituted or unsubstituted diphenylamino group, a substituted orunsubstituted N-(1-naphthyl)-N-phenylamino group, a substituted orunsubstituted N-(2-naphthyl)-N-phenylamino group, and the like.Furthermore, as for the diarylamino group, aryl groups may be directlybonded to faun a carbazole ring or they may be bonded through nitrogen,oxygen, or sulfur to form a ring. A hole-accepting unit in that case isa substituted or unsubstituted 9H-carbazol-9-yl group, a substituted orunsubstituted 10H-phenoxazin-10-yl group, a substituted or unsubstituted10H-phenothiazin-10-yl group, a substituted or unsubstituted5,10-dihydrophenazin-5-yl group.

Note that in the case where the above monohetero 5-membered aromaticring group and diarylamino group each have another substituent, thefollowing can be given as the substituent: an aryl group such as aphenyl group, tolyl group, or a naphthyl group; a heteroaryl group suchas a pyridyl group, a quinolyl group, or an isoquinolyl group; an alkylgroup such as a methyl group, an ethyl group, an isopropyl group, atert-butyl group; and the like.

The above hole-accepting unit is selected as appropriate, whereby thepartial structure represented by b can be formed.

As specific examples of the partial structure b in the case where themonohetero 5-membered aromatic ring group (note that monohetero5-membered aromatic ring includes a condensed aromatic hydrocarbon and anitrogen-containing 6-membered condensed aromatic ring) is applied asthe hole-accepting unit H_(A), the following can be given:4-(1-methyl-5-phenyl-1H-pyrrol-2-yl)phenyl group,4-(1,5-diphenyl-1H-pyrrol-2-yl)phenyl group,4-(2,5-diphenyl-1H-pyrrol-1-yl)phenyl group, 4-(5-phenyl-2-furyl)phenylgroup, 4-(5-phenyl-2-thienyl)phenyl group, 4-(1H-indol-1-yl)phenylgroup, 4-(2-methyl-1H-indol-1-yl)phenyl group,4-(2-phenyl-1H-indol-1-yl)phenyl group, 4-(1-phenyl-1H-indol-2-yl)phenylgroup, 4-(2-benzofuryl)phenyl group, 4-(2-benzothienyl)phenyl group,4-(2,3-diphenylisoindol-1-yl)phenyl group, 4-(3-phenylisofuryl)phenylgroup, 4-(3-phenylisothienyl)phenyl group, and the like.

As specific examples of the partial structure b in the case where thediarylamino group (a case where aryl groups are directly bonded to forma carbazole ring or a case where aryl groups are bonded throughnitrogen, oxygen, or sulfur is included) is applied as thehole-accepting unit H_(A), the following can be given:4-(diphenylamino)phenyl group, a4-[N-(biphenyl-4-yl)-N-phenylamino]phenyl group, a4-{N-[4-(1-naphthyl)phenyl]-N-phenylamino}phenyl group, a4-{N-[4-(2-naphthyl)phenyl]-N-phenylamino}phenyl group, a4-{N,N-bis[4-(1-naphthyl)phenyl]amino}phenyl group, a4-[N-(1-naphthyl)-N-phenylamino]phenyl group, a4-(9H-carbazol-9-yl)phenyl group, a 4-(3-phenyl-9H-carbazol-9-yl)phenylgroup, a 4-[3-(1-naphthyl)-9H-carbazol-9-yl]phenyl group, a4-[3-(2-naphthyl)-9H-carbazol-9-yl]phenyl group, a4-(10-phenyl-5,10-dihydrophenazin-5-yl)phenyl group, a4-(10H-phenoxazin-10-yl)phenyl group, a 4-(10H-phenothiazin-10-yl)phenylgroup, and the like.

Note that in the partial structure b, the hole-accepting unit H_(A) maybe bonded to carbon of α2 to form a ring. A specific example of thatcase is described below. As shown below, when a diphenylamino group isselected as the hole-accepting unit H_(A), the partial structure bbecomes a 4-(diphenylamino)phenyl group (Structural Formula (21)). Inthis 4-(diphenylamino)phenyl group (Structural Formula (21)), when thehole-accepting unit H_(A) and carbon of α2 are bonded, the partialstructure b becomes a 9-phenyl-9H-carbazol-3-yl group (StructuralFormula (22)). Thus, the partial structure b of Embodiment 1 includesthe 9-phenyl-9H-carbazol-3-yl group. This is just an example, and thesame modification can be applied to the cases where other hole-acceptingunits H_(A) are selected.

The organic semiconductor material of Embodiment 1 has a bipolarproperty having both an electron-transporting property and ahole-transporting property. Thus, in the case where the organicsemiconductor material is applied to a light-emitting element, drivingvoltage can be reduced. In the case where the organic semiconductormaterial is applied especially to a light-emitting layer, a prominenteffect can be obtained.

Further, in the case where the organic semiconductor material ofEmbodiment 1 is used as a host material of a light-emitting layer,localization of a light-emitting region can be suppressed, andconcentration quenching of a substance having a high light-emittingproperty or quenching due to triplet-triplet annihilation (T-Tannihilation) can be suppressed. Accordingly, high emission efficiencycan be realized.

Further, since the organic semiconductor material of Embodiment 1 hastwo ortho-linked benzene rings in the center, it has a sterically bulkystructure. The sterically bulky structure makes it difficult for theorganic semiconductor material to be crystallized in the case of beingformed as a film. Thus, the organic semiconductor material of Embodiment1 easily keeps an amorphous state in a thin film state, and thus issuitable for a light-emitting element.

In addition, the organic semiconductor material of Embodiment 1 has hightriplet excitation energy. Thus, the organic semiconductor material canbe used for a light-emitting element together with a phosphorescentcompound. Especially in the case where the organic semiconductormaterial is used together with a phosphorescent compound which exhibitslight emission of a short wavelength, a prominent effect can beobtained.

Moreover, the organic semiconductor material of Embodiment 1 has a largeenergy gap (a difference between the highest occupied molecular orbital(HOMO level) and the lowest unoccupied molecular orbital level (LUMOlevel)). Thus, the organic semiconductor material can be used for alight-emitting element together with a fluorescent compound. Especiallyin the case where the organic semiconductor material is used togetherwith a fluorescent compound which exhibits light emission of a shortwavelength, a prominent effect can be obtained.

Furthermore, in the organic semiconductor material of Embodiment 1, theelectron-accepting unit and the hole-accepting unit are bonded with atwisted quaterphenylene skeleton whose conjugation is hardly extendedtherebetween; thus, the molecular weight can be increased withoutdecrease in triplet excitation energy, and at the same time a stericallybulky molecular skeleton can be structured. In addition, the organicsemiconductor material can have a large band gap. Such a material isused for a light-emitting element, whereby the film quality can bestabilized.

Embodiment 2

In Embodiment 2, a benzoxazole derivative having the structurerepresented by General Formula (G1) will be described as an example ofthe organic semiconductor material of an embodiment of the presentinvention described in Embodiment 1.

A benzoxazole derivative according to Embodiment 2 is a benzoxazolederivative represented by General Formula (BOX1).

In the formula, Ar¹ and Ar² each independently represent a substitutedor unsubstituted aryl group having 6 to 13 carbon atoms, and R¹ to R⁴each independently represent any of hydrogen, an alkyl group having 1 to4 carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen. Ar¹ and carbon of α, or Ar¹ and Ar² may be bonded directlyor through sulfur, oxygen, or nitrogen.

The benzoxazole derivative according to Embodiment 2 is a benzoxazolederivative represented by General Formula (BOX2).

In the formula, R¹ to R⁴ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, an unsubstituted aryl grouphaving 6 to 10 carbon atoms, or halogen, and R¹¹ to R²⁰ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, or a substituted or unsubstituted aryl group having 6 to13 carbon atoms. A carbon atom of the benzene ring which is bonded toR¹¹ and carbon of α, or a carbon atom of the benzene ring which isbonded to R¹⁵ and a carbon atom of the benzene ring which is bonded toR²⁰ may be directly bonded.

The benzoxazole derivative according to Embodiment 2 is a benzoxazolederivative represented by General Formula (BOX2).

In the formula, R¹ to R⁴ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, an unsubstituted aryl grouphaving 6 to 10 carbon atoms, or halogen, and R¹¹ to R²⁰ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, a substituted or unsubstituted aryl group having 6 to 13carbon atoms. A carbon atom of the benzene ring which is bonded to R¹¹and carbon of α, or a carbon atom of the benzene ring which is bonded toR¹⁵ and a carbon atom of the benzene ring which is bonded to R²⁰ may bedirectly bonded to form a carbazole skeleton.

The benzoxazole derivative according to Embodiment 2 is a benzoxazolederivative represented by General Formula (BOX3).

In the formula, R¹¹ to R²⁰ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, or a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. A carbon atom ofthe benzene ring which is bonded to R¹¹ and carbon of α, or a carbonatom of the benzene ring which is bonded to R¹⁵ and a carbon atom of thebenzene ring which is bonded to R²⁰ may be directly bonded to form acarbazole skeleton.

Note that the number of carbon atoms of the aryl group or the arylenegroup described in this specification represents the number of carbonatoms which form a ring of the main skeleton, and the number of carbonatoms of a substituent bonded to the main skeleton is not includedtherein. As a substituent bonded to the aryl group or the arylene group,an alkyl group having 1 to 4 carbon atoms, an aryl group having 6 to 13carbon atoms, or a haloalkyl group having 1 carbon atom can be given.Specifically, a methyl group, an ethyl group, a propyl group, a butylgroup, a phenyl group, a naphthyl group, a fluorenyl group, atrifluoromethyl group, and the like are given. Further, the number ofsubstituents included in the aryl group or the arylene group may beeither single or plural. In the case where the aryl group or the arylenegroup has two substituents, the substituents may be bonded to each otherto form a ring. For example, when the aryl group is a fluorenyl group,carbon at the 9-position may have two phenyl groups, and the two phenylgroups may be bound to each other to form a spiro ring structure.

In General Formulae (BOX1) to (BOX3), the aryl group having 6 to 13carbon atoms may have a substituent, and in the case where the arylgroup has a plurality of substituents, the substituents may be bonded toform a ring. In addition, also in the case where one carbon atom has twosubstituents, the substituents may be bonded to form a spiro ring. Forexample, substituents represented by Structural Formulae (11-1) to(11-22) are given as specific examples of the groups represented by Ar¹and Ar².

For example, substituents represented by Structural Formulae (13-1) to(13-16) are given as specific examples of the groups represented by R¹to R⁴ and R¹¹ to R²⁰.

For example, substituents represented by Structural Formulae (14-1) to(14-18) are given as specific examples of the groups represented by R¹¹to R²⁰.

Further, in the benzoxazole derivatives represented by General Formulae(BOX1) to (BOX3), Ar¹ and Ar² are preferably a phenyl group in terms ofeasiness of synthesis and purification.

As specific examples of the benzoxazole derivatives represented byGeneral Formlae (BOX1) to (BOX3), benzoxazole derivatives represented byStructural Formulae (101) to (194), Structural Formulae (201) to (294),and Structural Formulae (301) to (383) can be given. However, thepresent invention is not limited thereto.

As a synthesis method of the benzoxazole derivatives of Embodiment 2, avariety of reactions can be applied. For example, the benzoxazolederivatives can be synthesized by any of synthesis reactions shown inSynthetic Schemes (1), (1-2), (2), (3), and (4).

<Synthesis of a Halogenated Benzoxazole Compound (Compound A)>

A halogenated benzoxazole compound (Compound A) can be synthesized as inSynthesis Scheme (1). In other words, the halogenated benzoxazolecompound (Compound A) can be obtained in such a manner that ahalogenated benzoxazole compound (Compound Al) and arylboronic acid orits derivative are coupled by the Suzuki-Miyaura coupling using apalladium catalyst.

In Synthesis Scheme (1), X¹ and X² represent halogen or a triflategroup; as the halogen, iodine, bromine, and chlorine are given; and X¹and X² may represent the same element or different elements. Inaddition, R¹ to R⁴ represents any of hydrogen, an alkyl group having 1to 4 carbon atoms, an unsubstituted aryl group having 6 to 10 carbonatoms, or halogen. R⁹⁰ and R⁹¹ represent a hydrogen atom or an alkylgroup having 1 to 6 carbon atoms and may be bonded to each other to forma ring when R⁹⁰ and R⁹¹ each are an alkyl group. A palladium catalystthat can be used in Synthesis Scheme (1) may be, but not limited to,palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), or thelike. A ligand of the palladium catalyst that can be used in SynthesisScheme (1) may be, but not limited to, tri(o-tolyl)phosphine,triphenylphosphine, tricyclohexylphosphine, or the like.

Examples of a base that can be used in Synthesis Scheme (1) include, butnot limited to, an organic base such as sodium tert-butoxide and aninorganic base such as potassium carbonate. As a solvent that can beused in Synthesis Scheme (1), a mixed solvent of toluene and water; amixed solvent of toluene, an alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, an alcohol suchas ethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, an alcohol such as ethanol, and water; a mixedsolvent of an ether such as ethylene glycol dimethyl ether and water; orthe like can be given. A mixed solvent of toluene and water or a mixedsolvent of toluene, ethanol, and water is more preferable.

Besides Synthesis Scheme (1), a synthesis method such as SynthesisScheme (1-2) is given as the synthesis method of the halogenatedbenzoxazole compound (Compound A).

<Synthesis of a Halogenated Benzoxazole Compound (Compound B)>

A halogenated benzoxazole compound (Compound B) can be synthesized as inSynthesis Scheme (1-2). In other words, the halogenated benzoxazolecompound (Compound B) can be obtained in such a manner that boronic acidof a halogenated benzoxazole compound or its derivative (Compound al)and dihalogenated benzene (Compound a2) are coupled by theSuzuki-Miyaura coupling using a palladium catalyst.

In Synthesis Scheme (1-2), X¹ and X² represent halogen or a triflategroup; as the halogen, iodine, bromine, and chlorine are given; and X¹and X² may represent the same element or different elements. Inaddition, R¹ to R⁴ represents any of hydrogen, an alkyl group having 1to 4 carbon atoms, an unsubstituted aryl group having 6 to 10 carbonatoms, or halogen. R⁹² and R⁹³ represent a hydrogen atom or an alkylgroup having 1 to 6 carbon atoms and may be bonded to each other to forma ring when R⁹² and R⁹³ each are an alkyl group. A palladium catalystthat can be used in Synthesis Scheme (1-2) may be, but not limited to,palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), or thelike. A ligand of the palladium catalyst that can be used in thesynthesis scheme (1-2) may be, but not limited to,tri(o-tolyl)phosphine, triphenylphosphine, tricyclohexylphosphine, orthe like.

Examples of a base that can be used in Synthesis Scheme (1-2) include,but not limited to, an organic base such as sodium tert-butoxide and aninorganic base such as potassium carbonate. In Synthesis Scheme (1-2),as a solvent that can be used, a mixed solvent of toluene and water; amixed solvent of toluene, an alcohol such as ethanol, and water; a mixedsolvent of xylene and water; a mixed solvent of xylene, an alcohol suchas ethanol, and water; a mixed solvent of benzene and water; a mixedsolvent of benzene, an alcohol such as ethanol, and water; a mixedsolvent of an ether such as ethylene glycol dimethyl ether and water; orthe like can be given. A mixed solvent of toluene and water or a mixedsolvent of toluene, ethanol, and water is more preferable.

<Synthesis of a Halogenated Arylamine Compound (Compound B)>

A halogenated arylamine compound (Compound B) can be synthesized as inSynthesis Scheme (2). In other words, the halogenated arylamine compound(Compound B) can be obtained in such a manner that a compound (CompoundB1) in which boronic acid of a tertiary arylamine compound or itsderivative and dihalogenated aryl (Compound B2) are coupled by theSuzuki-Miyaura coupling using a palladium catalyst. In Synthesis Scheme(2), X¹ and X² represents halogen or a triflate group; as the halogen,iodine, bromine, and chlorine are given; and X¹ and X² may represent thesame element or different elements. In addition, Ar¹ and Ar² eachindependently represent a substituted or unsubstituted aryl group having6 to 13 carbon atoms. R⁹⁴ and R⁹⁵ represent a hydrogen atom or an alkylgroup having 1 to 6 carbon atoms and may be bonded to each other to forma ring when R⁹⁴ and R⁹⁵ each are an alkyl group.

A palladium catalyst that can be used in Synthesis Scheme (1) may be,but not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0), or the like. A ligand of thepalladium catalyst that can be used in the synthesis scheme (2) may be,but not limited to, tri(o-tolyl)phosphine, triphenylphosphine,tricyclohexylphosphine, or the like. Examples of a base that can be usedin Synthesis Scheme (2) include, but not limited to, an organic basesuch as sodium tert-butoxide and an inorganic base such as potassiumcarbonate. In Synthesis Scheme (2), as a solvent that can be used, amixed solvent of toluene and water; a mixed solvent of toluene, analcohol such as ethanol, and water; a mixed solvent of xylene and water;a mixed solvent of xylene, an alcohol such as ethanol, and water; amixed solvent of benzene and water; a mixed solvent of benzene, analcohol such as ethanol, and water; a mixed solvent of an ether such asethylene glycol dimethyl ether and water; or the like can be given. Amixed solvent of toluene and water or a mixed solvent of toluene,ethanol, and water is more preferable.

<Synthesis of a Tertiary Arylamine Boronic Acid or its Derivative(Compound C)>

A tertiary arylamine boronic acid or its derivative (Compound C) can besynthesized as in Synthesis Scheme (3). In other words, a tertiary amineboronic acid (Compound C) can be obtained in such a manner that atertiary amine compound (Compound B) is transformed to a boronic acidusing an alkyllithium reagent and a boronic ester.

R¹⁰⁰ represents an alkyl group having 1 to 6 carbon atoms. R⁹⁶represents an alkyl group having 1 to 6 carbon atoms. As thealkyllithium reagent, n-butyllithium, methyllithium, or the like can beused. As the boronic ester, trimethyl borate, isopropyl borate, or thelike can be used. A boronic acid moiety of Compound C may be protectedby ethylene glycol or pinacol.

A benzoxazole compound (Compound D) can be synthesized as in SynthesisScheme (4). In other words, a tertiary aryl amine compound (Compound D)can be obtained in such a manner that a halogenated benzoxazole compound(Compound A) and the boronic acid of the tertiary amine (Compound C) arecoupled by the Suzuki-Miyaura coupling using a palladium catalyst. InSynthesis Scheme (4), X² represents halogen or a triflate group, andiodine, bromine, and chlorine are given as the halogen. In addition, Ar¹and Ar² each independently represent any of a substituted orunsubstituted aryl group having 6 to 13 carbon atoms, and R¹ to R⁴ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen. In Synthesis Scheme (4), an organoboron compound which isobtained by protecting the boronic acid moiety of Compound by ethyleneglycol or pinacol may be used instead of Compound C.

A palladium catalyst that can be used in Synthesis Scheme (4) may be,but not limited to, palladium(II) acetate,tetrakis(triphenylphosphine)palladium(0), or the like. A ligand of thepalladium catalyst that can be used in the synthesis scheme (2) may be,but not limited to, tri(o-tolyl)phosphine, triphenylphosphine,tricyclohexylphosphine, or the like. Examples of a base that can be usedin Synthesis Scheme (4) include, but not limited to, an organic basesuch as sodium tert-butoxide and an inorganic base such as potassiumcarbonate. In Synthesis Scheme (4), as a solvent that can be used, amixed solvent of toluene and water; a mixed solvent of toluene, analcohol such as ethanol, and water; a mixed solvent of xylene and water;a mixed solvent of xylene, an alcohol such as ethanol, and water; amixed solvent of benzene and water; a mixed solvent of benzene, analcohol such as ethanol, and water; a mixed solvent of an ether such asethylene glycol dimethyl ether and water; or the like can be given. Amixed solvent of toluene and water or a mixed solvent of toluene,ethanol, and water is more preferable.

In the above manner, the benzoxazole derivatives of Embodiment 2 can besynthesized.

Since the benzoxazole derivative of Embodiment 2 has a very large bandgap, light emission with favorable color purity can be obtained. Inaddition, the benzoxazole derivative of Embodiment 2 is a bipolarmaterial having a hole-transporting property and anelectron-transporting property and has a large band gap.

Further, as for the benzoxazole derivative of Embodiment 2, abenzoxazole skeleton having an electron-transporting property and askeleton having a hole-transporting property are bonded with a twistedquaterphenylene skeleton whose conjugation is hardly extendedtherebetween, whereby the molecular weight can be increased with hightriplet excitation energy maintained. Thus, the benzoxazole derivativecan have high electrochemical and thermal stabilities. Therefore, use ofthe benzoxazole derivative of Embodiment 2 makes it possible to improvereliability of a light-emitting element.

The benzoxazole derivative of Embodiment 2 can be used by itself as ahost material as well as an emission center material for alight-emitting layer, and a structure is employed in which a dopantmaterial which serves as a light-emitting substance is dispersed in thebenzoxazole derivative of Embodiment 2, whereby light emission with goodcolor purity from the dopant material can be efficiently obtained.

Further, the benzoxazole derivative of Embodiment 2 can also be used fora light-emitting substance by being dispersed as a dopant material in amaterial (a host material) having a larger band gap than the benzoxazolederivative of Embodiment 2, whereby light emission from the benzoxazolederivative of Embodiment 2 can be obtained.

The benzoxazole derivative of Embodiment 2 can be used as acarrier-transporting material for a functional layer of a light-emittingelement. For example, the benzoxazole derivative can be used for ahole-transporting layer, a hole-injecting layer, anelectron-transporting layer, or an electron-injecting layer. In thisspecification, a layer formed of a substance with a highcarrier-injecting property or a substance with a highcarrier-transporting property is also referred to as a functional layerwhich has functions of injecting and transporting carriers, or the like.

The benzoxazole derivative of Embodiment 2 is used for a light-emittingelement, whereby a light-emitting element with high efficiency, highreliability, and a long life can be obtained.

Embodiment 3

In Embodiment 3, an oxadiazole derivative having the structurerepresented by General Formula (G1) will be described as an example ofthe organic semiconductor material of an embodiment of the presentinvention described in Embodiment 1.

An oxadiazole derivative of Embodiment 3 is an oxadiazole derivativerepresented by General Formula (OXD1).

In the formula, Ar¹¹, Ar¹², and Ar¹³ represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. In addition, Ar¹¹and carbon of α, or Ar¹¹ and Ar¹² may be bonded to each other directlyor through any of oxygen, sulfur, or nitrogen.

Further, the oxadiazole derivative of Embodiment 3 is preferably anoxadiazole derivative represented by General Formula (OXD2).

In the formula, R³¹ to R⁴⁰ each independently represent any of hydrogen,an alkyl group having 1 to 4 carbon atoms, or an unsubstituted arylgroup having 6 to 13 carbon atoms, and Ar¹³ represents a substituted orunsubstituted aryl group having 6 to 13 carbon atoms. In addition, acarbon atom of the benzene ring which is bonded to R³¹ and carbon of a,or a carbon atom of the benzene ring which is bonded to R³⁵ and a carbonatom of the benzene ring which is bonded to R⁴⁰ may be directly bondedto each other to form a carbazole skeleton.

In General Formula (OXD1) and General Formula (OXD2), as substituentsrepresented by Ar¹¹, Ar¹², and Ar¹³, for example, substituentsrepresented by Structural Formulae (15-1) to (15-16) are given. As asubstituent bonded to Ar¹¹, Ar¹², and Ar¹³, an alkyl group having 1 to 4carbon atoms or an unsubstituted aryl group having 6 to 13 carbon atomsis given. Specifically, a methyl group, an ethyl group, a propyl group,a butyl group, a phenyl group, a naphthyl group, a fluorenyl group, andthe like are given. Further, the number of substituents included in thearyl group may be either single or plural. In the case where the arylgroup has two substituents, the substituents may be bonded to each otherto form a ring. A ring structure may be a spiro ring.

Note that in General Formula (OXD2), Ar¹³ is preferably an aryl grouphaving an alkyl group having 1 to 4 carbon atoms, or an unsubstitutedphenyl group or naphthyl group having 6 to 10 carbon atoms as shown inStructural Formulae (15-4) to (15-8) and (15-12) to (15-15), and is morepreferably an unsubstituted phenyl group or naphthyl group as shown inStructural Formulae (15-1), (15-4), and (15-5).

Further, in General Formula (OXD2), as substituents represented by R³¹to R⁴⁰, for example, substituents represented by Structural Formulae(12-1) to (12-25) are given.

For example, specific examples of the oxadiazole derivatives ofEmbodiment 3 include, but not limited to, oxadiazole derivativesrepresented by Structural Formulae (421) to (533).

The oxadiazole derivative represented by General Formula (OXD1) can besynthesized by synthesis methods represented by Synthesis Schemes (11)to (14) below. Hereinafter, an example of a synthesis method of theoxadiazole derivative of Embodiment 3 will be described.

First, a halogenated oxadiazole derivative (Compound 5) is synthesized.Synthesis Scheme (11) is shown below.

In Synthesis Scheme (11), a halogenated aryl derivative (Compound 1) andhydrazine are reacted to synthesize halogenated aryl hydrazide (Compound2). Note that in Synthesis Scheme (11), the hydrazine may be a hydrazinehydrate. Next, the halogenated aryl hydrazide (Compound 2) and arylcarboxylic acid halide (Compound 3) are reacted to obtain a diacylhydrazine derivative (Compound 4). A halogenated oxadiazole derivative(Compound 5) can be obtained by ring closure by dehydration of thediacyl hydrazine derivative (Compound 4) using a dehydrating agent toform a 1,3,4-oxadiazole ring. Note that in Synthesis Scheme (11), Rrepresents an alkoxy group having 1 to 4 carbon atoms or halogen, Ar¹³represents an aryl group having 6 to 10 carbon atoms, and X¹ and X²represents a halogen group. X¹ is preferably a bromo group or an iodinegroup, and X² is preferably a chloro group.

Note that phosphoryl chloride, thionyl chloride, or the like can be usedas the dehydrating agent.

A method for synthesizing the halogenated oxadiazole derivative(Compound 5) is not limited to above Synthesis Scheme (11), and otherknown methods can also be used.

Next, an electron-accepting unit in the oxadiazole derivative ofEmbodiment 3 is synthesized. Specifically, a halogenated oxadiazolecompound represented by Compound 7 is synthesized. Synthesis Scheme(12-a) is shown below.

The halogenated oxadiazole compound (Compound 5) and an arylboronic acidor its derivative (Compound 6) are coupled by the Suzuki-Miyauracoupling using a palladium catalyst, whereby a halogenated oxadiazolecompound (Compound 7) can be obtained.

In Synthesis Scheme (12-a), X¹ and X² represent halogen or a triflategroup, and as the halogen, iodine, bromine, and chlorine are given. Inaddition, X¹ and X² may represent the same element or differentelements. Further, in Synthesis Scheme (12-a), R⁹⁰ represents hydrogenor an alkyl group having 1 to 6 carbon atoms, and R⁹¹ representshydrogen or an alkyl group having 1 to 6 carbon atoms. R⁹⁰ and R⁹¹ maybe bonded to each other to form a ring.

A palladium catalyst that can be used in Synthesis Scheme (12-a) may bepalladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), or thelike. As a ligand of the palladium catalyst that can be used in thesynthesis scheme (12-a), tri(o-tolyl)phosphine, triphenylphosphine,tricyclohexylphosphine, and the like are given. As a base that can beused in Synthesis Scheme (1), an organic base such as sodiumtert-butoxide and an inorganic base such as potassium carbonate aregiven.

As a solvent that can be used in Synthesis Scheme (12-a), a mixedsolvent of toluene and water; a mixed solvent of toluene, an alcoholsuch as ethanol, and water; a mixed solvent of xylene and water; a mixedsolvent of xylene, an alcohol such as ethanol, and water; a mixedsolvent of benzene and water; a mixed solvent of benzene, an alcoholsuch as ethanol, and water; a mixed solvent of an ether such as ethyleneglycol dimethyl ether and water; or the like can be given. Note that amixed solvent of toluene and water or a mixed solvent of toluene,ethanol, and water is more preferable.

Note that the synthesis method of the halogenated oxadiazole compoundrepresented by Compound 7 is not limited to the synthesis method shownin Synthesis Scheme (12-a). The halogenated oxadiazole compound may besynthesized by, for example, a synthesis method shown in SynthesisScheme (12-b) below.

A boronic acid or its derivative (Compound 8) and dihalogenated arylcompound (Compound 9) are coupled by the Suzuki-Miyaura coupling using apalladium catalyst, whereby the halogenated oxadiazole compound(Compound 7) can be obtained.

In Synthesis Scheme (12-b), X¹ and X² represent halogen or a triflategroup, and as the halogen, iodine, bromine, or chlorine is given. Inaddition, X¹ and X² may represent the same element or differentelements. Further, in Synthesis Scheme (12-a), R⁹² represents hydrogenor an alkyl group having 1 to 6 carbon atoms, and R⁹³ representshydrogen or an alkyl group having 1 to 6 carbon atoms. R⁹² and R⁹³ maybe bonded to each other to form a ring.

A palladium catalyst that can be used in Synthesis Scheme (12-b) may bepalladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), or thelike. As a ligand of the palladium catalyst that can be used in thesynthesis scheme (12-b), tri(o-tolyl)phosphine, triphenylphosphine,tricyclohexylphosphine, and the like are given. Examples of a base thatcan be used in Synthesis Scheme (12-b) include an organic base such assodium tert-butoxide and an inorganic base such as potassium carbonate.

As a solvent that can be used in Synthesis Scheme (12-b), a mixedsolvent of toluene and water; a mixed solvent of toluene, an alcoholsuch as ethanol, and water; a mixed solvent of xylene and water; a mixedsolvent of xylene, an alcohol such as ethanol, and water; a mixedsolvent of benzene and water; a mixed solvent of benzene, an alcoholsuch as ethanol, and water; a mixed solvent of an ether such as ethyleneglycol dimethyl ether and water; or the like can be given. A mixedsolvent of toluene and water or a mixed solvent of toluene, ethanol, andwater is more preferable.

Next, a hole-accepting unit in the oxadiazole derivative of Embodiment 3is synthesized. Synthesis Schemes (13-1) and (13-2) are shown below.

A boronic acid of a tertiary arylamine or its derivative (Compound 10)and dihalogenated aryl compound (Compound 9) are coupled by theSuzuki-Miyaura coupling using a palladium catalyst, whereby ahalogenated arylamine compound (Compound 11) is synthesized (SynthesisScheme (13-1)).

In Synthesis Scheme (13-1), X¹ and X² represent halogen or a triflategroup, and as the halogen, iodine, bromine, and chlorine are given. Inaddition, X¹ and X² may represent the same element or differentelements. Further, Ar¹¹ Ar¹² represent a substituted or unsubstitutedaryl group having 6 to 13 carbon atoms. R⁹⁴ and R⁹⁵ each represent anhydrogen atom or an alkyl group having 1 to 6 carbon atoms.

As a palladium catalyst that can be used in Synthesis Scheme (13-1) maybe palladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), andthe like are given. As a ligand of the palladium catalyst that can beused in the synthesis scheme (13-1), tri(o-tolyl)phosphine,triphenylphosphine, tricyclohexylphosphine, and the like are given.

Examples of a base that can be used in Synthesis Scheme (13-1) includean organic base such as sodium tert-butoxide and an inorganic base suchas potassium carbonate. As a solvent that can be used in SynthesisScheme (13-1), a mixed solvent of toluene and water; a mixed solvent oftoluene, an alcohol such as ethanol, and water; a mixed solvent ofxylene and water; a mixed solvent of xylene, an alcohol such as ethanol,and water; a mixed solvent of benzene and water; a mixed solvent ofbenzene, an alcohol such as ethanol, and water; a mixed solvent of anether such as ethylene glycol dimethyl ether and water; or the like canbe given. Note that a mixed solvent of toluene and water or a mixedsolvent of toluene, ethanol, and water is more preferable.

Next, a tertiary amine boronic acid (Compound 12) can be obtained insuch a manner that a halogenated aryl amine compound (Compound 11) istransformed to a boronic acid using an alkyllithium reagent and aboronic ester (Synthesis Scheme (13-2)).

In Synthesis Scheme (13-2), R¹⁰⁰ represents an alkyl group having 1 to 6carbon atoms. R⁹⁶ represents an alkyl group having 1 to 6 carbon atoms.A boronic acid moiety of Compound 12 may be protected by ethylene glycolor pinacol.

In Synthesis Scheme (13-2), n-butyllithium, methyllithium, or the likecan be used as the alkyllithium reagent. Trimethyl borate, isopropylborate, or the like can be used as the boronic ester.

Next, Compound 7 and Compound 12 are coupled to synthesize theoxadiazole derivative of Embodiment 3 represented by General Formula(OXD1). Synthesis Scheme (14) is shown below.

The halogenated oxadiazole derivative (Compound 7) and the boronic acidof the tertiary amine (Compound 12) are coupled by the Suzuki-Miyauracoupling using a palladium catalyst, whereby the oxadiazole derivativeof Embodiment 3 represented by General Formula (OXD1) can be obtained.

In Synthesis Scheme (14), X² represents halogen or a triflate group, andas the halogen, iodine, bromine, and chlorine are given. In addition,Ar¹¹, Ar¹², and Ar¹³ represent a substituted or unsubstituted aryl grouphaving 6 to 13 carbon atoms.

A palladium catalyst that can be used in Synthesis Scheme (14) may bepalladium(II) acetate, tetrakis(triphenylphosphine)palladium(0), or thelike. As a ligand of the palladium catalyst that can be used in thesynthesis scheme (14), tri(o-tolyl)phosphine, triphenylphosphine,tricyclohexylphosphine, and the like are given. Examples of a base thatcan be used in Synthesis Scheme (14) include an organic base such assodium tert-butoxide and an inorganic base such as potassium carbonate.

As a solvent that can be used in Synthesis Scheme (14), a mixed solventof toluene and water; a mixed solvent of toluene, an alcohol such asethanol, and water; a mixed solvent of xylene and water; a mixed solventof xylene, an alcohol such as ethanol, and water; a mixed solvent ofbenzene and water; a mixed solvent of benzene, an alcohol such asethanol, and water; a mixed solvent of an ether such as ethylene glycoldimethyl ether and water; or the like can be given. A mixed solvent oftoluene and water or a mixed solvent of toluene, ethanol, and water ismore preferable. Further, instead of Compound 12, a compound obtained byprotecting the boronic acid moiety of Compound 12 with an alkyl groupmay be used.

In the above manner, the oxadiazole derivative of Embodiment 3 can besynthesized.

The oxadiazole derivative of Embodiment 3 has high excitation energy,and an electron-transporting and hole-transporting properties.Therefore, it can be favorably used for a light-emitting element. Inparticular, the oxadiazole derivative of Embodiment 3 is preferably usedfor the light-emitting layer because the balance between injectedelectrons and holes is important for efficient emission of alight-emitting element. Since the oxadiazole derivative of Embodiment 3has high triplet excitation energy, it can be used for a light-emittinglayer together with a substance which emits phosphorescence.

Further, since singlet excitation energy (a difference in energy betweena ground state and a singlet excited state) is higher than tripletexcitation energy, a substance having high triplet excitation energyalso has high singlet excitation energy. Therefore, the oxadiazolederivative of Embodiment 3 having high triplet excitation energy isuseful even in the case of being used for a light-emitting layertogether with a substance which emits fluorescence.

Further, as for the oxadiazole derivative of Embodiment 3, an oxadiazoleskeleton having an electron-transporting property and a skeleton havinga hole-transporting property are bonded with a twisted quaterphenyleneskeleton whose conjugation is hardly extended therebetween, whereby themolecular weight can be increased with high triplet excitation energymaintained. Thus, the oxadiazole derivative can have highelectrochemical and thermal stabilities. Therefore, use of theoxadiazole derivative of Embodiment 3 makes it possible to improvereliability of a light-emitting element.

Further, the oxadiazole derivative of Embodiment 3 can transportcarriers, and therefore can be used for a carrier-transporting layer ina light-emitting element. In particular, the oxadiazole derivative ofEmbodiment 3 has high triplet excitation energy; therefore, energytransfer from a light-emitting layer does not easily occur even in thecase where the oxadiazole derivative of Embodiment 3 is used for a layerin contact with the light-emitting layer. Accordingly, high emissionefficiency can be achieved.

Embodiment 4

In Embodiment 4, one mode of a light-emitting element in which theorganic semiconductor material described in Embodiments 1 to 3 is usedwill be described with reference to FIG. 1 and FIG. 2.

A light-emitting element of Embodiment 4 has a plurality of layersbetween a pair of electrodes. The plurality of layers are stacked bycombination of layers formed of a substance having a highcarrier-injecting property and a substance having a highcarrier-transporting property so that a light-emitting region is formedapart from the electrodes, or so that carriers are recombined in aportion apart from the electrodes.

In Embodiment 4, the light-emitting element includes a first electrode102, a second electrode 104, and an EL layer which is provided betweenthe first electrode 102 and the second electrode 104. Note that inEmbodiment 4, description will be made below assuming that the firstelectrode 102 functions as an anode and the second electrode 104functions as a cathode. In other words, description will be made belowassuming that light emission can be obtained when voltage is applied tothe first electrode 102 and the second electrode 104 so that thepotential of the first electrode 102 is higher than that of the secondelectrode 104.

A substrate 101 is used as a support of the light emitting element. Thesubstrate 101 can be made of, for example, glass, plastic, metal, or thelike. Note that the substrate 101 may be made of materials other thanglass or plastic as long as it can function as a support of thelight-emitting element. Note that when light emission from thelight-emitting element is extracted outside through the substrate 101,the substrate 101 is preferably a light-transmitting substrate.

The first electrode 102 is preferably formed using any of metals,alloys, or conductive compounds, a mixture thereof, or the like with ahigh work function (specifically, a work function of greater than orequal to 4.0 eV is preferable). For example, indium tin oxide (ITO),indium tin oxide containing silicon or silicon oxide, indium zinc oxide(IZO), indium oxide containing tungsten oxide and zinc oxide (IWZO), andthe like are given. Such a conductive metal oxide film is usually formedby a sputtering method, but may also be formed by an ink-jet method, aspin coating method, or the like by application of a sol-gel method orthe like. For example, indium zinc oxide (IZO) can be formed by asputtering method using indium oxide into which 1 wt % to 20 wt % ofzinc oxide is added, as a target. Indium oxide containing tungsten oxideand zinc oxide (IWZO) can be formed by a sputtering method using atarget in which 0.5 wt % to 5 wt % of tungsten oxide and 0.1 wt % to 1wt % of zinc oxide are mixed with indium oxide. Other than those, gold(Au), platinum (Pt), nickel (Ni), tungsten (W), chromium (Cr),molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd),titanium (Ti), nitrides of the metal materials (such as titaniumnitride: TiN), and the like are given.

In the case where a layer containing a composite material describedbelow is used as a layer in contact with the first electrode 102,various metals, alloys, electrically conductive compounds, or a mixturethereof can be used for the first electrode 102 regardless of the workfunction. For example, aluminum (Al), silver (Ag), an aluminum alloy(such as AlSi), or the like can be used. Besides, an element thatbelongs to Group 1 or 2 of the periodic table which has a low workfunction, i.e., alkali metals such lithium (Li) and cesium (Cs) andalkaline earth metals such as magnesium (Mg), calcium (Ca), andstrontium (Sr); alloys of them (e.g., MgAg and AlLi); rare earth metalssuch as europium (Eu) and ytterbium (Yb); alloys of them; and the likecan also be used. A film of an alkali metal, an alkaline earth metal, oran alloy including these can be formed by a vacuum evaporation method.In addition, an alloy including an alkali metal or an alkaline earthmetal can be formed by a sputtering method. Further, a silver paste orthe like can be formed by an ink-jet method.

The EL layer 103 described in Embodiment 4 includes a hole-injectinglayer 111, a hole-transporting layer 112, a light-emitting layer 113, anelectron-transporting layer 114, and an electron-injecting layer 115.The EL layer 103 includes at least a light-emitting layer, and there isno particular limitation on a structure of the other stacked layers. Inother words, there is no particular limitation on the stacked structureof layers of the EL layer 103; layers formed of a substance having ahigh electron-transporting property, a substance having a highhole-transporting property, a substance having a high electron-injectingproperty, a substance having a high hole-injecting property, a bipolarsubstance (a substance having high electron-transporting andhole-transporting properties), a substance having a high light-emittingproperty may be combined with the organic semiconductor materialdescribed in Embodiments 1 to 3 as appropriate to form the EL layer 103.For example, the EL layer 103 may be formed by any combination of ahole-injecting layer, a hole-transporting layer, a light-emitting layer,an electron-transporting layer, an electron-injecting layer, and thelike, as appropriate. Materials for forming layers will be specificallygiven below.

The hole-injecting layer 111 is a layer containing a substance having ahigh hole-injecting property. As a substance having a highhole-injecting property, molybdenum oxide, vanadium oxide, rutheniumoxide, tungsten oxide, manganese oxide, or the like can be used.Besides, as a low molecular organic compound, the following compoundsare given: phthalocyanine-based compounds such as phthalocyanine (H₂Pc),copper(II) phthalocyanine (CuPc), and vanadyl phthalocyanine (VOPc);aromatic amine compounds such as4,4′,4″-tris(N,N-diphenylamino)triphenylamine (TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine (MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(DNTPD), 1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(DPA3B), 3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(PCzPCA2), and3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(PCzPCN1), and the like.

Alternatively, for the hole-injecting layer 111, a composite material inwhich an acceptor substance is mixed into a substance having a highhole-transporting property can be used. Note that when a material formedby mixing an acceptor substance into a substance with a highhole-transporting property is used, materials for forming the electrodecan be selected regardless of the work function. In other words, besidesa material with a high work function, a material with a low workfunction may also be used as the first electrode 102. Such a compositematerial can be formed by co-deposition of a substance with a highhole-transporting property and an acceptor substance.

Note that, in this specification, “composition” means not only a simplemixture of two materials but also a mixture of a plurality of materialsin a condition where an electric charge is given and received among thematerials.

As the organic compound used for the composite material, a variety ofcompounds such as an aromatic amine compound, a carbazole derivative,aromatic hydrocarbon, and a high molecular compound (oligomer,dendrimer, polymer, or the like) can be used. An organic compound usedfor the composite material is preferably an organic compound having ahigh hole-transporting property. Specifically, a substance having a holemobility of higher than or equal to 10⁻⁶ cm²/Vs is preferably used.However, any substance other than the above substances may also be usedas long as it is a substance whose hole-transporting property is higherthan the electron-transporting property. Organic compounds that can beused for the composite material is specifically given below.

As the organic compound that can be used for the composite material, thefollowing can be given, for example: aromatic amine compounds such asMTDATA, TDATA, DPAB, DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB or α-NPD), andN,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(TPD); carbazole derivatives such as 4,4′-di(N-carbazolyl)biphenyl(CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene (TCPB),9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (CzPA), and1,4-bis[4-(N-carbazolyl)phenyl-2,3,5,6-tetraphenylbenzene; and aromatichydrocarbon compounds such as 2-tert-butyl-9,10-di(2-naphthyl)anthracene(t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (t-BuDBA),9,10-di(2-naphthyl)anthracene (DNA), 9,10-diphenylanthracene (DPAnth),2-tert-butylanthracene (t-BuAnth),9,10-bis(4-methyl-1-naphthyl)anthracene (DMNA),9,10-bis[2-(1-naphthyl)phenyl)-2-tert-butyl-anthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene,2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene,2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (DPVBi), and9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene (DPVPA).

As an acceptor substance, organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F₄-TCNQ) andchloranil, and a transition metal oxide can be given. In addition,oxides of metals that belong to Group 4 to Group 8 of the periodic tablecan be given. Specifically, vanadium oxide, niobium oxide, tantalumoxide, chromium oxide, molybdenum oxide, tungsten oxide, manganeseoxide, and rhenium oxide are preferable because of a highelectron-accepting property. Among those, molybdenum oxide is especiallypreferable since it is stable in the air, has a low hygroscopicproperty, and is easily handled.

Further, for the hole-injecting layer 111, a high molecular compound(oligomer, dendrimer, polymer, or the like) can be used. For example,the following high molecular compounds are given: poly(N-vinylcarbazole)(PVK), poly(4-vinyltriphenylamine) (PVTPA),poly[N-(4-{N′-[4-(4-diphenylamino)phenyl]phenyl-N′-phenylamino}phenyl)methacrylamide](PTPDMA), and poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine](Poly-TPD). In addition, a high molecular compound doped with acid suchas poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid)(PEDOT/PSS) or polyaniline/poly(styrenesulfonic acid) (PAni/PSS) can beused.

Note that the hole-injecting layer 111 can be formed using a compositematerial of the above high molecular compound, such as PVK, PVTPA,PTPDMA, or Poly-TPD, and the above acceptor substance.

The hole-transporting layer 112 is a layer containing a substance havinga high hole-transporting property. As the substance having a highhole-transporting property, the following low molecular organic compoundcan be used: an aromatic amine compound such as NPB (or α-NPD), TPD,4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl (DFLDPBi),or 4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]-biphenyl(BSPB); 4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(m-MTDATA);N-[4-(9H-carbazol-9-yl)phenyl]-N-phenyl-spiro-9,9′-bifluoren-2-amine(YGASF),N,N′-bis[4-(9H-carbazol-9-yl)phenyl-N,N′-diphenylvinyl-4,4′-diamine(YGABP); 4-(9H-carbazol-9-yl)-2′-phenyltriphenylamine (o-YGA1BP);4-(9H-carbazol-9-yl)-3′-phenyltriphenylamine (m-YGA1BP);4-(9H-carbazol-9-yl)-4′-phenyltriphenylamine (p-YGA1BP);1,3,5-tris(N-carbazolyl)benzene (TCzB); or4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA). The substances givenhere are mainly substances each having an electron mobility of higherthan or equal to 10⁻⁶ cm²/Vs. However, any substance other than theabove substances may also be used as long as it is a substance whosehole-transporting property is higher than the electron-transportingproperty. The layer containing a substance having a highhole-transporting property is not limited to a single layer, and two ormore layers containing the above materials may also be stacked.

Furthermore, for the hole-transporting layer 112, a composite materialin which an acceptor substance is contained in the above substancehaving a high hole-transporting property can be used.

Alternatively, for the hole-transporting layer 112, a high molecularcompound such as PVK, PVTPA, PTPDMA, or Poly-TPD can be used.

The light-emitting layer 113 is a layer containing a substance having ahigh light-emitting property, and a variety of materials can be used forthe light-emitting layer 113. As the substance having a highlight-emitting property, for example, a fluorescent compound which emitsfluorescence or a phosphorescent compound which emits phosphorescencecan be used. In addition, plural types of substances having a highlight-emitting property may be used without limitation to one type.

Examples of a phosphorescent compound that can be used for thelight-emitting layer are given below. As a light-emitting material forblue and blue-tinged light emission, the following are given:bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)tetrakis(1-pyrazolyl)borate(FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C²′]iridium(III)picolinate(FIrpic),bis[2-(3′,5′bistrifluoromethylphenyl)pyridinato-N,C²′]iridium(III)picolinate(Ir(CF₃ppy)₂(pic)),bis[2-(4′,6′-difluoropheny)pyridinato-N,C²′]iridium(III)acetylacetonate(FIracac) and the like. As a light-emitting material for green andgreen-tinged light emission, the following are given:tris(2-phenylpyridinato-N,C^(2′))iridium(III) (Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III)acetylacetonate(Ir(pbi)₂(acac)), bis(benzo[h]quinolinato)iridium(III)acetylacetonate(Ir(bzq)₂(acac)), and the like. As a light-emitting material for yellowand yellow-tinged light emission, the following are given:bis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III)acetylacetonate(Ir(dpo)₂(acac)),bis[2-(4′-perfluorophenylphenyl)pyridinato]iridium(III)acetylacetonate(Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III)acetylacetonate(Ir(bt)₂(acac)), and the like. As a light-emitting material for orangeand orange-tinged light emission, the following are given:tris(2-phenylquinolinato-N,C^(2′))iridium(III) (Ir(pq)₃),bis(2-phenylquinolinato-N,C^(2′))iridium(III)acetylacetonate(Ir(pq)₂(acac)), and the like. As a light-emitting material for red andred-tinged light emission, the following organometallic complex aregiven:bis[2-(2′-benzo[4,5-α]thienyl)pyridinato-N,C^(3′))iridium(III)acetylacetonate(Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III)acetylacetonate(Ir(piq)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(Ir(Fdpq)₂(acac)),2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II) (PtOEP), andthe like are given. In addition, a rare-earth metal complex such astris(acetylacetonato)(monophenanthroline)terbium(III) (Tb(acac)₃(Phen)),tris(1,3-diphenyl-1,3-propanedionato)(monophenanthroline)europium(III)(Eu(DBM)₃(Phen)), ortris[1-(2-thenoyl)-3,3,3-trifluoroacetonato](monophenanthroline)europium(III)(Eu(TTA)₃(Phen)) performs light emission (electron transition betweendifferent multiplicities) from a rare-earth metal ion; therefore, such arare-earth metal complex can be used as the phosphorescent compound.

Examples of a fluorescent compound that can be used for thelight-emitting layer are given below. As a light-emitting material forblue and blue-tinged light emission, the following are given:N,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine((YGA2S), 4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(YGAPA), 4-(9H-carbazol-9-yl)-4′-(9,10-diphenyl-2-anthryl)triphenylamine(2YGAPPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(PCAPA), perylene, 2,5,8,11-tetra-tert-butylperylene (TBP),4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(PCBAPA), and the like. As a light-emitting material for green andgreen-tinged light emission, the following are given:N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine (2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(2YGABPhA), N,N,9-triphenylanthracen-9-amine (DPhAPhA), and the like. Asa light-emitting material for yellow and yellow-tinged light emission,rubrene, 5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (BPT), andthe like are given. As a light-emitting material for red and red-tingedlight emission, the following are given:N,N,N′,N′-tetrakis(4-methylphenyl)tetracene-5,11-diamine (p-mPhTD),7,13-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine (p-mPhAFD), and the like.

Note that the light-emitting layer may have a structure in which any ofthe above substances having a high light-emitting property (guestmaterial) is dispersed into another substance (host material). A varietyof types of substances can be used for a material for dispersing thelight-emitting substance (host material), and it is preferable to use asubstance whose lowest unoccupied molecular orbital (LUMO) level ishigher than that of a substance having a high light-emitting property(guest material) and whose highest occupied molecular orbital (HOMO)level is lower than that of the substance having a high light-emittingproperty (guest material). Note that in this specification, “the HOMOlevel or the LUMO level is high” means that the energy level is high,while “the HOMO level or the LUMO level is low” means that the energylevel is low. For example, Substance A having a HOMO level of −5.5 eVhas the HOMO level which is lower by 0.3 eV than Substance B having aHOMO level of −5.2 eV and higher by 0.2 eV than Substance C having aHOMO level of −5.7 eV.

The organic semiconductor material described in Embodiments 1 to 3 has alarge band gap and a bipolar property, and thus is suitable as a hostmaterial. The organic semiconductor material described in Embodiments 1to 3 has a large band gap; thus, light emission from a guest materialcan be efficiently obtained even in the case where a guest materialwhich exhibits light emission of a short wavelength is used. Inaddition, the driving voltage of the light-emitting element can bereduced.

Further, the organic semiconductor material described in Embodiments 1to 3 has high triplet excitation energy; thus, light emission from aguest material can be efficiently obtained even in the case where aphosphorescent compound is used as a guest material. Especially in thecase where a phosphorescent compound which exhibits light emission of ashort wavelength is used, a prominent effect can be obtained.

Plural types of materials can be used as the host material. For example,in order to suppress crystallization, a substance which suppressescrystallization, such as rubrene, may be further added. In addition,NPB, Alq, or the like may be further added so that energy is transferredmore efficiently to the substance with a light-emitting property.

The structure in which a substance having a high light-emitting property(guest material) is dispersed in another substance (host material) isused for the light-emitting layer, whereby crystallization of thelight-emitting layer 113 can be suppressed. In addition, concentrationquenching due to the increase in concentration of the substance having ahigh light-emitting property (guest material) can also be suppressed.

The electron-transporting layer 114 is a layer containing a substancehaving a high electron-transporting property. As a low molecular organiccompound, for example, a metal complex such astris(8-quinolinolato)aluminum(III) (Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq),bis(8-quinolinolato)zinc(II) (Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (ZnPBO), orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (ZnBTZ) can be used. Further,besides the above metal complex, a heterocyclic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD),1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene (OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (TAZ01),2,2′,2″-(1,3,5-benzenetriyl)-tris(1-phenyl-1H-benzimidazole) (TPBI),bathophenanthroline (BPhen), or bathocuproine (BCP) can be used. Thesubstances described here are mainly materials having an electronmobility of higher than or equal to 10⁻⁶ cm²/Vs. Note that theelectron-transporting layer 114 may be formed of substances other thanthose described above as long as the substances have higherelectron-transporting properties than hole-transporting properties.Further, the electron-transporting layer 114 may be formed as not only asingle-layer structure but also a layered structure in which two or morelayers foinied of the above substances are stacked.

For the electron-transporting layer 114, a high molecular compound canbe used. For example,poly[(9,9-dihexylfluorene-2,7-diyl)-co-(pyridine-3,5-diyl)] (PF-Py),poly[(9,9-dioctylfluorene-2,7-diyl)-co-(2,2′-bipyridine-6,6′-diyl)](PF-BPy), or the like can be used.

The electron-injecting layer 115 is a layer containing a substancehaving a high electron-injecting property. As the substance having ahigh electron-injecting property, an alkali metal or an alkaline earthmetal such as lithium (Li) or magnesium (Mg), or a compound thereof suchas lithium fluoride (LiF), cesium fluoride (CsF), or calcium fluoride(CaF₂) can be used. For example, a layer formed of a material having anelectron-transporting property containing an alkali metal, an alkalineearth metal, or a compound thereof, such as a layer formed of Alq whichcontains magnesium (Mg), may be used. It is preferable to use a layer ofa substance having an electron-transporting property containing analkali metal or an alkaline earth metal as the electron-injecting layerbecause electron injection from the second electrode 104 is efficientlyperformed.

As a substance for forming the second electrode 104, a metal, an alloy,an electrically conductive compound, a mixture thereof, or the like witha low work function (specifically, a work function of lower than orequal to 3.8 eV is preferable) can be used. As a specific example ofsuch a cathode material, an element that belongs to Group 1 or 2 in theperiodic table, that is, an alkali metal such as lithium (Li) or cesium(Cs); an alkaline earth metal such as magnesium (Mg), calcium (Ca), orstrontium (Sr); an alloy containing the element that belongs to Group 1or 2 (such as MgAg, AlLi); a rare-earth metal such as europium (Eu) orytterbium (Yb); an alloy thereof; or the like can be used. A film of analkali metal, an alkaline earth metal, or an alloy including these canbe formed by a vacuum evaporation method. In addition, an alloyincluding an alkali metal or an alkaline earth metal can be formed by asputtering method. Further, the second electrode 104 can be formed byapplying a silver paste or the like by an ink-jet method.

In the case where the electron-injecting layer 115 has a function ofpromoting electron injection is provided between the second electrode104 and the electron-transporting layer 114, the second electrode 104can be formed using a variety of conductive materials such as Al, Ag,ITO, and indium tin oxide containing silicon or silicon oxide,regardless of their work functions. These conductive materials can beformed by a sputtering method, an ink jet method, a spin coating method,or the like.

Note that since the organic semiconductor material described inEmbodiment 1 exhibits blue light emission, it can be used for thelight-emitting layer as a substance having a high light-emittingproperty. For example, the oxadiazole derivative described in Embodiment3 exhibits light emission ranging from purple to blue, and thus can befavorably used for the light-emitting element as a substance having ahigh light-emitting property. In addition, the organic semiconductormaterial described in Embodiments 1 to 3 has a bipolar property, andthus can also be used for layers other than the light-emitting layer(e.g., the hole-transporting layer and the electron-transporting layer).Moreover, the organic semiconductor material described in Embodiments 1to 3 has a large band gap, and thus can also be used for anelectron-blocking layer or a hole-blocking layer. Furthermore, theorganic semiconductor material described in Embodiments 1 to 3 has hightriplet excitation energy, and thus can also be used for anexciton-blocking layer.

As a formation method of the EL layer, a variety of methods can be usedregardless of a dry process or a wet process. For example, a vacuumevaporation method, an ink-jet method, a spin coating method, or thelike may be used. In addition, the electrodes or the layers may beformed by different deposition methods.

For example, the EL layer may be formed using a high molecular compoundby a wet process. Alternatively, the EL layer can be formed using a lowmolecular organic compound by a wet process. Further alternatively, theEL layer may be formed using a low molecular organic compound by a dryprocess such as a vacuum evaporation method.

The electrode may be formed using a sol-gel method by a wet method, orusing a paste of a metal material by a wet method. Alternatively, theelectrode may be formed by a dry process such as a sputtering method ora vacuum evaporation method.

For example, in the case where the light-emitting element of Embodiment4 is applied to a display device and the display device is manufacturedusing a large substrate, the light-emitting layer is preferably formedby a wet process. When the light-emitting layer is formed by an inkjetmethod, selective deposition of the light-emitting layer for each colorcan be easily performed even when a large substrate is used.

In the light-emitting element of Embodiment 4 having the abovestructure, current flows by provision of a potential difference betweenthe first electrode 102 and the second electrode 104 and holes andelectrons are recombined in the EL layer 103, whereby light is emitted.

The emitted light is extracted through one or both of the firstelectrode 102 and the second electrode 104. Accordingly, one or both ofthe first electrode 102 and the second electrode 104 is/are an electrodehaving a light-transmitting property. For example, when only the firstelectrode 102 has a light-transmitting property, the emitted light isextracted from the substrate side through the first electrode 102. Inthe case where only the second electrode 104 is a light-transmittingelectrode, light is extracted from the side opposite to the substratethrough the second electrode 104. In the case where both the firstelectrode 102 and the second electrode 104 are light-transmittingelectrodes, emitted light is extracted from both the substrate side andthe side opposite to the substrate through the first electrode 102 andthe second electrode 104.

The structure of the layers provided between the first electrode 102 andthe second electrode 104 is not limited to the above structure. Anystructure other than the above structure can be employed as long as alight-emitting region for recombination of holes and electrons ispositioned away from the first electrode 102 and the second electrode104 so as to prevent quenching caused by proximity of the light-emittingregion to metal, and the organic semiconductor material described inEmbodiment 1 is provided.

In other words, there is no particular limitation on the stackedstructure of the layers; layers formed of a substance having a highelectron-transporting property, a substance having a highhole-transporting property, a substance having a high electron-injectingproperty, a substance having a high hole-injecting property, a bipolarsubstance (a substance having high electron-transporting andhole-transporting properties), and the like may be combined with theorganic semiconductor material described in Embodiments 1 to 3 asappropriate to form the stacked structure.

For example, as illustrated in FIG. 2, a structure may be employed inwhich the second electrode 104 functioning as a cathode, the EL layer103, and the first electrode 102 functioning as an anode are stacked inthis order over the substrate 101. In FIG. 2, a structure in which theelectron-injecting layer 115, the electron-transporting layer 114, thelight-emitting layer 113, the hole-transporting layer 112, and thehole-injecting layer 111 are stacked in this order over the secondelectrode 104 is employed.

Note that in Embodiment 4, the light-emitting element is formed over asubstrate made of glass, plastic, or the like. Formation of a pluralityof such light-emitting elements over one substrate enables formation ofa passive matrix light-emitting device. Alternatively, for example, athin film transistor (TFT) may be formed over a substrate made of glass,plastic, or the like, and a light-emitting element may be manufacturedover an electrode that is electrically connected to the TFT. Thus, anactive matrix light-emitting device which controls driving of alight-emitting element by a TFT can be manufactured. There is noparticular limitation on the structure of the TFT. The TFT may be eitherof staggered type or of inverted staggered type. In addition, a drivingcircuit formed over a TFT substrate may be formed using an N-type TFTand a P-type TFT, or may be formed using any one of an N-type TFT and aP-type TFT. In addition, there is also no particular limitation on thecrystallinity of a semiconductor film used for the TFT. Either anamorphous semiconductor film or a crystalline semiconductor film may beused for the TFT. Alternatively, a single crystalline semiconductor filmmay be used. The single crystalline semiconductor film can be formed bySmart Cut (registered trademark) or the like.

Note that Embodiment 4 can be combined with any of the other embodimentsas appropriate.

Embodiment 5

In this embodiment, a mode of a light-emitting element in which aplurality of light-emitting units according to an embodiment of thepresent invention are stacked (hereinafter, such a light-emittingelement is also referred to as a stacked type element) will be describedwith reference to FIG. 3. This light-emitting element is a stacked typelight-emitting element that has a plurality of light-emitting unitsbetween a first electrode and a second electrode. The structure of eachof the light-emitting units can be similar to that described inEmbodiment 4. In other words, the light-emitting element described inEmbodiment 4 is a light-emitting element having one light-emitting unit.In this embodiment, a light-emitting element having a plurality oflight-emitting units will be described.

In FIG. 3, a first light-emitting unit 511 and a second light-emittingunit 512 are stacked between a first electrode 501 and a secondelectrode 502. A charge generating layer 513 is provided between thefirst light-emitting unit 511 and the second light-emitting unit 512. Asthe first electrode 501 and the second electrode 502, electrodes similarto those in Embodiment 4 can be applied. In addition, the firstlight-emitting unit 511 and the second light-emitting unit 512 may havethe same structure or different structures. Structures of the firstlight-emitting unit 511 and the second light-emitting unit 512 can besimilar to the structure described in Embodiment 4.

The charge generating layer 513 is a layer that injects electrons intoone of the light-emitting units and injects holes into the other of thelight-emitting units when a voltage is applied to the first electrode501 and the second electrode 502. The charge generating layer 513 mayhave a single-layer structure or a stacked-layer structure. As a stackedstructure of plural layers, a structure in which a hole-injecting layerand an electron-injecting layer are stacked is preferable.

As the hole-injecting layer, a semiconductor or an insulator, such asmolybdenum oxide, vanadium oxide, rhenium oxide, or ruthenium oxide, canbe used. Alternatively, the hole-injecting layer may have a structure inwhich an acceptor substance is added into a substance having a highhole-transporting property. The layer including a substance having ahigh hole-transporting property and an acceptor substance is formedusing the composite material described in Embodiment 4 and includes, asan acceptor substance,7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (F₄-TCNQ) or metaloxide such as vanadium oxide, molybdenum oxide, or tungsten oxide. Asthe substance having a high hole-transporting property, any of variouscompounds such as aromatic amine compounds, carbazole derivatives,aromatic hydrocarbons, and high molecular compounds (such as oligomers,dendrimers, and polymers) can be used. Note that a substance having ahole mobility of 10⁻⁶ cm²/Vs or higher is preferably used as thesubstance having a high hole-transporting property. However, anysubstance other than the above substances may also be used as long as itis a substance in which the hole-transporting property is higher thanthe electron-transporting property. Since the composite material whichincludes the substance having a high hole-transporting property and theacceptor substance is superior in carrier-injecting property andcarrier-transporting property, low-voltage driving and low-currentdriving can be realized.

As the electron-injecting layer, an insulator or a semiconductor, suchas lithium oxide, lithium fluoride, or cesium carbonate, can be used.Alternatively, the electron-injecting layer may have a structure inwhich a donor substance is added into a substance having a highelectron-transporting property. As the donor substance, an alkali metal,an alkaline earth metal, a rare earth metal, a metal that belongs toGroup 13 of the periodic table, or an oxide or carbonate of them can beused. Specifically, lithium (Li), cesium (Cs), magnesium (Mg), calcium(Ca), ytterbium (Yb), indium (In), lithium oxide, cesium carbonate, orthe like is preferably used. Alternatively, organic compound such astetrathianaphthacene may be used for the donor substance. As thesubstance having a high electron-transporting property, the materialsdescribed in Embodiment 4 can be used. Note that a substance having anelectron mobility of 10⁻⁶ cm²/Vs or higher is preferably used as thesubstance having a high electron-transporting property. Note that anysubstance that has a higher electron-transporting property than ahole-transporting property may be used other than the above substances.Since the composite material of the substance having a highelectron-transporting property and the donor substance has excellentcarrier-injecting and carrier-transporting properties, low-voltagedriving and low-current driving can be realized.

Further, the electrode materials described in Embodiment 4 can be usedfor the charge generating layer 513. For example, the charge generatinglayer 513 may be formed with a combination of a layer including asubstance having a high hole-transporting property and metal oxide witha transparent conductive film. Note that a layer having a highlight-transmitting property is preferably used as the charge generatinglayer in terms of light extraction efficiency.

In any case, the charge generating layer 513, which is interposedbetween the first light-emitting unit 511 and the second light-emittingunit 512, is acceptable as long as electrons are injected to one of thelight-emitting units and holes are injected to the other of thelight-emitting units when a voltage is applied to the first electrode501 and the second electrode 502. For example, in a case of applying avoltage so that a potential of the first electrode is higher than apotential of the second electrode, any structure is acceptable for thecharge generating layer 513 as long as the charge generating layer 513injects electrons and holes into the first light-emitting unit 511 andthe second light-emitting unit 512, respectively.

Although the light-emitting element having two light-emitting units isdescribed in this embodiment, a light-emitting element in which three ormore light-emitting units are stacked can be applied in a similar way.By arranging a plurality of light-emitting units between a pair ofelectrodes so as to be partitioned by a charge generating layer as inthe light-emitting element of this embodiment, the element can performlight emission in a high luminance region while keeping a currentdensity low; whereby the element can have long life. Moreover, alight-emitting device with low power consumption, which can be driven atlow voltage, can be achieved.

The light-emitting units emit light of different colors from each other,thereby obtaining light emission of a desired color as the wholelight-emitting element. For example, in a light-emitting element havingtwo light-emitting units, the emission colors of the firstlight-emitting unit and the second light-emitting unit are madecomplementary, so that the light-emitting element which emits whitelight as the whole element can be obtained. Note that “complementarycolor” means a relation between colors which becomes an achromatic colorwhen they are mixed. That is, white light emission can be obtained bymixture of lights obtained from substances emitting the lights ofcomplementary colors. The same can be applied to a light-emittingelement having three light-emitting units. For example, when the firstlight-emitting unit emits red light, the second light-emitting unitemits green light and the third light-emitting unit emits blue light,white light can be emitted from the whole light-emitting element.

Note that this embodiment can be combined with another embodiment asappropriate.

Embodiment 6

In this embodiment, a light-emitting device having a light-emittingelement of an embodiment of the present invention which is described inthe above embodiment will be described.

In this embodiment, a light-emitting device having a light-emittingelement of an embodiment of the present invention in a pixel portionwill be described with reference to FIGS. 4A and 4B. Note that FIG. 4Ais a top view of the light-emitting device and FIG. 4B is across-sectional view taken along line A-A′ and line B-B′ in FIG. 4A.This light-emitting device includes a driver circuit portion (sourceside driver circuit) 601 and a driver circuit portion (gate side drivercircuit) 603 which are indicated by dotted lines in order to control thelight emission of the light-emitting element provided in a pixel portion602. Further, a reference numeral 604 represents a sealing substrate, areference numeral 605 represents a sealant, and the inside surrounded bythe sealant 605 is a space 607.

Note that a leading wiring 608 is a wiring for transmitting signalsinput in the source side driver circuit 601 and the gate side drivercircuit 603. The leading wiring 608 receives video signals, clocksignals, start signals, reset signals, and the like from an FPC(flexible printed circuit) 609 that serves as an external inputterminal. Although only the FPC is illustrated here, this FPC may beprovided with a printed wiring board (PWB). The light-emitting device inthis specification includes in its category not only a light-emittingdevice itself but also a light-emitting device with an FPC or a PWBattached thereto.

Next, a sectional structure of the light-emitting device will bedescribed with reference to FIG. 4B. The driver circuit portion and thepixel portion are formed over an element substrate 610. In this case,one pixel in the pixel portion 602 and the source side driver circuit601 which is the driver circuit portion are illustrated.

Note that as the source side driving circuit 601, a CMOS circuit inwhich an n-channel TFT 623 and a p-channel TFT 624 are combined isformed. The driver circuit may be formed by various CMOS circuits, PMOScircuits, or NMOS circuits. In this embodiment, a driver-integrated typein which a driver circuit is formed over the substrate provided with thepixel portion is described; however, the present invention is notlimited to this type, and the driver circuit can be formed outside thesubstrate.

The pixel portion 602 includes a plurality of pixels each having aswitching TFT 611, a current controlling TFT 612, and a first electrode613 that is electrically connected to a drain of the current controllingTFT 612. Note that an insulator 614 is formed to cover an end portion ofthe first electrode 613. Here, the insulator 614 is aimed using apositive photosensitive acrylic resin.

In order to improve the coverage, the insulator 614 is provided suchthat either an upper edge portion or a lower edge portion of theinsulator 614 has a curved surface with a curvature. For example, whenpositive photosensitive acrylic is used as a material for the insulator614, it is preferable that only the upper edge portion of the insulator614 have a curved surface with a radius of curvature (0.2 μm to 3 μm).Further, the insulator 614 can be formed using either negativephotosensitive acrylic that becomes insoluble in an etchant due to lightirradiation, or positive photosensitive acrylic that becomes soluble inan etchant due to light irradiation.

An EL layer 616 and a second electrode 617 are formed over the firstelectrode 613. Here, various metals, alloys, electrically conductivecompounds, or mixtures thereof can be used for a material of the firstelectrode 613. If the first electrode 613 is used as an anode, it ispreferable that the first electrode be formed using a metal, an alloy,an electrically conductive compound, or a mixture thereof with a highwork function (preferably, a work function of 4.0 eV or higher) amongsuch materials. For example, the first electrode 613 can be formed usinga single-layer film of an indium tin oxide film containing silicon, anindium zinc oxide film, a titanium nitride film, a chromium film, atungsten film, a Zn film, a Pt film, or the like; or a stacked film,such as a stack of a titanium nitride film and a film containingaluminum as its main component or a three-layer structure of a titaniumnitride film, a film containing aluminum as its main component, and atitanium nitride film. Note that when a stacked structure is employed,the first electrode 613 has low resistance as a wiring, forms afavorable ohmic contact, and can serve as an anode.

The EL layer 616 is foliated by various methods such as an evaporationmethod using an evaporation mask, an inkjet method, a spin coatingmethod, or the like. The EL layer 616 includes the organic semiconductormaterial described in Embodiments 1 to 3. Any of low molecularcompounds, high molecular compounds, oligomers and dendrimers may beemployed as the material used for the EL layer 616. As the material forthe EL layer, not only an organic compound but also an inorganiccompound may be used.

As the material for the second electrode 617, various types of metals,alloys, electrically conductive compounds, and mixtures of these can beused. If the second electrode is used as a cathode, it is preferablethat the second electrode be formed using a metal, an alloy, anelectrically conductive compound, a mixture thereof, or the like with alow work function (preferably, a work function of 3.8 eV or lower) amongsuch materials. As an example, an element belonging to Group 1 or Group2 in the periodic table, i.e., an alkali metal such as lithium (Li) orcesium (Cs), an alkaline earth metal such as magnesium (Mg), calcium(Ca), or strontium (Sr), or an alloy containing any of these (such asMgAg or AILi); and the like can be given. If light generated in the ELlayer 616 is transmitted through the second electrode 617, the secondelectrode 617 can be formed using a stack of a metal thin film and atransparent conductive film (indium tin oxide (ITO), indium tin oxidecontaining silicon or silicon oxide, indium zinc oxide (IZO), indiumoxide containing tungsten oxide and zinc oxide (IWZO), or the like).

By attaching the sealing substrate 604 to the element substrate 610 withthe sealant 605, a light-emitting element 618 is provided in the space607 which is surrounded by the element substrate 610, the sealingsubstrate 604, and the sealant 605. Note that the space 607 is filledwith a filler such as an inert gas (e.g., nitrogen, argon, or the like)or the sealant 605.

As the sealant 605, an epoxy resin is preferably used. In addition, itis desirable to use a material that allows permeation of moisture oroxygen as little as possible. As the sealing substrate 604, a plasticsubstrate formed using FRP (Fiberglass-Reinforced Plastics), PVF(polyvinyl fluoride), polyester, acrylic, or the like can be usedbesides a glass substrate or a quartz substrate.

As described above, a light-emitting device having the light-emittingelement in Embodiment 4 or 5 can be obtained.

The light-emitting device described in this embodiment includes thelight-emitting element described in Embodiment 4 or 5. Thelight-emitting element described in Embodiment 4 or 5 has high emissionefficiency and the driving voltage is low. Therefore, a light-emittingdevice which can emit light with high luminance can be obtained.Further, a light-emitting device with low power consumption can beobtained.

As described above, an active-matrix light-emitting device whichcontrols driving of a light-emitting element with a transistor isdescribed in this embodiment; however, a passive-matrix light-emittingdevice may be used. FIGS. 5A and 5B illustrate a passive matrixlight-emitting device manufactured by applying an embodiment of thepresent invention. FIG. 5A is a perspective view of the light-emittingdevice, and FIG. 5B is a cross-sectional view taken along line X-Y inFIG. 5A. In FIGS. 5A and 5B, an EL layer 955 is provided between anelectrode 952 and an electrode 956 over a substrate 951. The edge of theelectrode 952 is covered with an insulating layer 953. A partition walllayer 954 is provided on the insulating layer 953. The sidewalls of thepartition wall layer 954 are aslope so that a distance between bothsidewalls is gradually narrowed toward the surface of the substrate. Inother words, a cross section taken along the direction of the short sideof the partition wall layer 954 is trapezoidal, and the lower side (aside which is in the same direction as a plane direction of theinsulating layer 953 and in contact with the insulating layer 953) isshorter than the upper side (a side which is in the same direction asthe plane direction of the insulating layer 953 and not in contact withthe insulating layer 953). A cathode can be patterned by providing thepartition wall layer 954 in this manner. In addition, in a passivematrix light-emitting device, a light-emitting device with low powerconsumption can be obtained by including a light-emitting element withhigh emission efficiency and low driving voltage according to anembodiment of the present invention.

Note that this embodiment can be combined with another embodiment asappropriate.

Embodiment 7

In this embodiment, an electronic device according to an embodiment ofthe present invention including the light-emitting device described inEmbodiment 6 as a part will be described. The electronic deviceaccording to an embodiment of the present invention has thelight-emitting element described in Embodiment 4 or 5, and thus has adisplay portion with low power consumption.

As examples of an electronic device manufactured using a light-emittingdevice according to an embodiment of the present invention, there are acamera such as a video camera or a digital camera, a goggle typedisplay, a navigation system, an audio reproducing device (a car audiocomponent, an audio component, or the like), a computer, a game machine,a portable information terminal (mobile computer, mobile phone, mobilegame machine, an electronic book, or the like), an image reproducingdevice having a recording medium (specifically, a device for reproducinga recording medium such as a digital versatile disc (DVD) and having adisplay device for displaying the reproduced image), and the like. FIGS.6A to 6E illustrate specific examples of these electronic devices.

FIG. 6A illustrates a television device of this embodiment, whichincludes a housing 9101, a supporting base 9102, a display portion 9103,speaker portions 9104, a video input terminal 9105, and the like. In thedisplay portion 9103 of this television device, light-emitting elementssimilar to those described in the above embodiments are arranged inmatrix. The light-emitting element has a feature that light emissionefficiency is high and power consumption is low. In addition, thelight-emitting element also has a feature that driving voltage thereofis low. The display portion 9103 which includes the light-emittingelement has similar features. Therefore, in this television device, lowpower consumption is achieved. With such features, a power supplycircuit can be significantly reduced or downsized in the televisiondevice; therefore, reduction in size and weight of the housing 9101 andthe supporting base 9102 can be achieved. As for the television deviceof this embodiment, less power consumption and reduction in size andweight are achieved; therefore, the television can be provided as aproduct which is suitable for living environment.

FIG. 6B illustrates a computer of this embodiment, which includes a mainbody 9201, a housing 9202, a display portion 9203, a keyboard 9204, anexternal connection port 9205, a pointing device 9206, and the like. Inthe display portion 9203 of this computer, light-emitting elementssimilar to those described in the above embodiments are arranged inmatrix. The light-emitting element has a feature that light emissionefficiency is high and power consumption is low. In addition, thelight-emitting element also has a feature that driving voltage thereofis low. The display portion 9103 which includes the light-emittingelement has similar features. Therefore, in this computer, low powerconsumption is achieved. With such features, a power supply circuit canbe significantly reduced or downsized in the computer; therefore,reduction in size and weight of the main body 9201 and the housing 9202can be achieved. As for the computer of this embodiment, low powerconsumption and reduction in size and weight are achieved; therefore,the computer can be provided as a product which is suitable forenvironment.

FIG. 6C illustrates a camera of this embodiment, which includes a mainbody 9301, a display portion 9302, a housing 9303, an externalconnection port 9304, a remote control receiving portion 9305, an imagereceiving portion 9306, a battery 9307, an audio input portion 9308,operation keys 9309, an eyepiece portion 9310, and the like. In thedisplay portion 9302 of this camera, light-emitting elements similar tothose described in the above embodiments are arranged in matrix. Thelight-emitting element has a feature that light emission efficiency ishigh and power consumption is low. In addition, the light-emittingelement also has a feature that driving voltage thereof is low. Thedisplay portion 9302 which includes the light-emitting element hassimilar features. Therefore, in the camera, low power consumption isachieved. With such features, a power supply circuit can besignificantly reduced or downsized in the camera; therefore, reductionin size and weight of the main body 9301 can be achieved. As for thecamera of this embodiment, low power consumption and reduction in sizeand weight are achieved; therefore, the camera can be provided as aproduct which is suitable for being carried.

FIG. 6D illustrates electronic paper according to the present inventionwhich is flexible and includes a main body 9660, a display portion 9661which displays images, a driver IC 9662, a receiver 9663, a film battery9664, and the like. The driver IC, the receiver, or the like may bemounted using a semiconductor component. In the electronic paper of thepresent invention, the main body 9660 is formed using a flexiblematerial such as plastic or a film. In the electronic paper, the displayportion 9661 has light-emitting elements similar to those described inEmbodiments 1 to 3, which are arranged in matrix. The light-emittingelements have features of a long lifetime and low power consumption.Since the display portion 9661 including the light-emitting elementsalso has similar features, the electronic paper has high reliability andlow power consumption thereof is achieved.

FIG. 6E illustrates a cellular phone of this embodiment which includes amain body 9401, a housing 9402, a display portion 9403, an audio inputportion 9404, an audio output portion 9405, operation keys 9406, anexternal connection port 9407, an antenna 9408, and the like. In thedisplay portion 9403 of this cellular phone, light-emitting elementssimilar to that described in Embodiment 2 are arranged in matrix. Thelight-emitting element has a feature that light emission efficiency ishigh and power consumption is low. In addition, the light-emittingelement also has a feature that driving voltage thereof is low. Thedisplay portion 9403 which includes the light-emitting element hassimilar features. Therefore, in the cellular phone, low powerconsumption is achieved. With such features, a power supply circuit canbe significantly reduced or downsized in the cellular phone; therefore,reduction in size and weight of the main body 9401 and the housing 9402can be achieved. As for the cellular phone of this embodiment, low powerconsumption and reduction in size and weight are achieved; therefore,the cellular phone can be provided as a product which is suitable forbeing carried.

FIGS. 12A to 12C illustrate an example of a structure of a cellularphone, which is different from a structure of the cellular phone of FIG.6E. FIG. 12A is a front view, FIG. 12B is a rear view, and FIG. 12C is adevelopment view. The cellular phone in FIGS. 12A to 12C is a so-calledsmartphone which has both functions of a phone and a portableinformation terminal, and incorporates a computer to conduct a varietyof data processing in addition to voice calls.

The cellular phone illustrated in FIGS. 12A to 12C has two housings 1001and 1002. The housing 1001 includes a display portion 1101, a speaker1102, a microphone 1103, operation keys 1104, a pointing device 1105, acamera lens 1106, an external connection terminal 1107, an earphoneterminal 1008, and the like, while the housing 1002 includes a keyboard1201, an external memory slot 1202, a camera lens 1203, a light 1204,and the like. In addition, an antenna is incorporated in the housing1001.

Further, in addition to the above structure, the cellular phone mayincorporate a non-contact IC chip, a small-sized memory device, or thelike.

In the display portion 1101, the light-emitting device described in theabove embodiment can be incorporated, and a display direction can beappropriately changed depending on the usage mode. The cellular phone isprovided with the camera lens 1106 on the same surface as the displayportion 1101; therefore, the cellular phone can be used as a videophone.Further, a still image and a moving image can be taken with the cameralens 1203 and the light 1204 using the display portion 1101 as aviewfinder. The speaker 1102 and the microphone 1103 can be used forvideo calls, recording, reproducing, and the like without being limitedto voice calls. With the use of the operation keys 1104, making andreceiving calls, inputting simple information such as e-mail or thelike, scrolling the screen, moving the cursor, and the like arepossible. Furthermore, the housing 1001 and the housing 1002 (FIG. 12A),which are overlapped with each other, are developed by sliding asillustrated in FIG. 12C, and can be used as a portable informationterminal. In this case, smooth operation can be conducted using thekeyboard 1201 and the pointing device 1105. The external connectionterminal 1107 can be connected to an AC adaptor and various types ofcables such as a USB cable, and charging, data communication with acomputer, and the like are possible. Furthermore, a large amount of datacan be stored and transferred by inserting a recording medium into theexternal memory slot 1202.

Further, in addition to the above functions, the cellular phone mayinclude an infrared communication function, a television receivingfunction, or the like.

FIG. 7 illustrates an audio reproducing device, specifically, a caraudio system, which includes a main body 701, a display portion 702, andoperation switches 703 and 704. The display portion 702 can be realizedwith the light-emitting device (passive matrix type or active matrixtype) described in the above embodiment. Further, the display portion702 may be formed using a segment type light-emitting device. In anycase, the use of a light-emitting element according to an embodiment ofthe present invention makes it possible to form a bright display portionwhile achieving less power consumption, with the use of a vehicle powersource (12 to 42 V). Further, although this embodiment describes anin-car audio system, a light-emitting device according to an embodimentof the present invention may also be used in portable audio systems oraudio systems for home use.

FIG. 8 illustrates a digital player as an example of an audioreproducing device. The digital player illustrated in FIG. 8 includes amain body 710, a display portion 711, a memory portion 712, an operationportion 713, earphones 714, and the like. Note that headphones orwireless earphones can be used instead of the earphones 714. The displayportion 711 can be realized with the light-emitting device (passivematrix type or active matrix type) described in the above embodiment.Further, the display portion 711 may be formed using a segment typelight-emitting device. In any case, the use of the light-emittingelement according to an embodiment of the present invention makes itpossible to form a bright display portion which can display images evenwhen using a secondary battery (a nickel-hydrogen battery or the like)while achieving less power consumption. As the memory portion 712, ahard disk or a nonvolatile memory is used. For example, by using aNAND-type nonvolatile memory with a recording capacity of 20 to 200gigabytes (GB), and operating the operation portion 713, an image or asound (music) can be recorded and reproduced. Note that in the displayportion 702 and the display portion 711, white characters are displayedagainst a black background, and thus, power consumption can be reduced.This is particularly effective for portable audio systems.

As described above, the applicable range of the light-emitting devicemanufactured by applying an embodiment of the present invention is sowide that the light-emitting device is applicable to electronic devicesin various fields. By applying an embodiment of the present invention,an electronic device which has a display portion consuming low power canbe manufactured.

A light-emitting device to which an embodiment of the present inventionis applied has a light-emitting element with high light emissionefficiency, and can also be used as a lighting device. A light-emittingdevice to which an embodiment of the present invention is applied canemit light with high luminance and is preferably used as a lightingdevice. One mode of using a light-emitting element to which anembodiment of the present invention is applied for a lighting devicewill be described with reference to FIG. 9.

FIG. 9 illustrates a liquid crystal display device using thelight-emitting device to which an embodiment of the present invention isapplied for a backlight, as an example of the electronic device using alight-emitting device according to an embodiment of the presentinvention for a lighting device. The liquid crystal display deviceillustrated in FIG. 9 includes a housing 901, a liquid crystal layer902, a backlight 903, and a housing 904, and the liquid crystal layer902 is connected to a driver IC 905. The light-emitting device to whichan embodiment of the present invention is applied is used for thebacklight 903, and current is supplied through a terminal 906.

Since the light-emitting device according to an embodiment of thepresent invention is thin and consumes less power, reduction inthickness and power consumption of a liquid crystal display device ispossible by using a light-emitting device according to an embodiment ofthe present invention as a backlight of the liquid crystal displaydevice. Moreover, a light-emitting device according to an embodiment ofthe present invention is a plane emission type lighting device, and canhave a large area. Therefore, the backlight can have a large area, and aliquid crystal display device having a large area can be obtained.

FIG. 10 illustrates an example in which a light-emitting deviceaccording to an embodiment of the present invention is used as a desklamp, which is one of lighting devices. The desk lamp illustrated inFIG. 10 includes a housing 2001 and a light source 2002, and alight-emitting device according to an embodiment of the presentinvention is used as the light source 2002. Since a light-emittingdevice according to an embodiment of the present invention consumes lesspower, the desk lamp also consumes less power.

FIG. 11 illustrates an example in which a light-emitting device to whichan embodiment of the present invention is applied is used as an interiorlighting device 3001. Since a light-emitting device according to anembodiment of the present invention can have a large area, alight-emitting device according to an embodiment of the presentinvention can be used as a lighting device having a large area.Moreover, since a light-emitting device according to an embodiment ofthe present invention consumes less power, a light-emitting deviceaccording to an embodiment of the present invention can be used as alighting device which consumes less power. Thus, a television device3002 according to an embodiment of the present invention such as thatillustrated in FIG. 6A may be placed in a room where a light-emittingdevice to which an embodiment of the present invention is applied isused as the interior lighting device 3001, and public broadcasting ormovies can be watched there. In such a case, since both devices consumelow power, environmental load can be reduced.

Note that this embodiment can be combined with another embodiment asappropriate.

Example 1

In this example, an example of an electron-accepting unit and ahole-accepting unit in an organic semiconductor material according to anembodiment of the present invention will be described.

As described in Embodiment 1, it is difficult to evaluate the electronaffinity and the ionization potential of an electron-accepting unit anda hole-accepting unit of an organic semiconductor material according toan embodiment of the present invention. Therefore, the electron affinityand the ionization potential of each unit were evaluated using acompound represented by General Formula (G2A) which corresponds to apartial structure a of an organic semiconductor material represented byGeneral Formula (G1). Further, the hole-accepting unit was evaluatedusing a compound represented by General Formula (G2B) which correspondsto a partial structure b of an organic semiconductor materialrepresented by General Formula (G1).

In this example, the electron affinity and the ionization potential wereestimated by cyclic voltammetry (CV) measurement by using2,5-diphenyl-1,3,4-oxadiazole and 2-phenylbenzoxazole which correspondto the partial structure a represented by General Formula (G2A).Structural formulae of 2,5-diphenyl-1,3,4-oxadiazole and2-phenylbenzoxazole which were measured in this example are shown below.

In this example, the electron affinity and the ionization potential werecalculated by cyclic voltammetry (CV) measurement by using9-phenyl-9H-carbazole and triphenylamine which correspond to the partialstructure b represented by General Formula (G2B). Structural foimulae of9-phenyl-9H-carbazole and triphenylamine which were measured in thisexample are shown below.

An electrochemical analyzer (ALS model 600A or 600C, manufactured by BASInc.) was used for the CV measurement. As a solution used for the CVmeasurement, dehydrated dimethylformamide (DMF, product of Sigma-AldrichInc., 99.8%, Catalog No. 22705-6) was used as a solvent, andtetra-n-butylammonium perchlorate (n-Bu₄NClO₄, product of Tokyo ChemicalIndustry Co., Ltd., Catalog No. T0836), which was a supportingelectrolyte, was dissolved in the solvent such that the concentration oftetra-n-butylammonium perchlorate was 100 mmol/L. Further, themeasurement object was also dissolved such that the concentrationthereof was 2 mmol/L. Further, as a working electrode, a platinumelectrode (a PTE platinum electrode, manufactured by BAS Inc.) was used.As an auxiliary electrode, a platinum electrode (a VC-3 Pt counterelectrode (5 cm), manufactured by BAS Inc.) was used. As a referenceelectrode, an Ag/Ag⁺ electrode (an RE7 nonaqueous solvent referenceelectrode, manufactured by BAS Inc.) was used. Note that the measurementwas conducted at a room temperature (20° C. to 25° C.). In addition, thescan speed at the CV measurement was 0.1 V/sec in all the measurements.

[Calculation of the Potential Energy of the Reference Electrode withRespect to the Vacuum Level]

First, potential energy (eV) of the reference electrode (Ag/Ag⁺electrode) used in this example with respect to the vacuum level wascalculated. That is, the Fermi level of the Ag/Ag⁺ electrode wascalculated. It is known that the oxidation-reduction potential offerrocene in methanol is +0.610 [V vs. SHE] with respect to a standardhydrogen electrode (Reference: Christian R. Goldsmith et al., J. Am.Chem. Soc., Vol. 124, No. 1, pp. 83-96, 2002). On the other hand, byusing the reference electrode used in this example, theoxidation-reduction potential of ferrocene in methanol was calculated tobe +0.11 [V vs. Ag/Ag⁺]. Therefore, it was found that the potentialenergy of the reference electrode used in this example was lower thanthat of the standard hydrogen electrode by 0.50 [eV].

Here, it is known that the potential energy of the standard hydrogenelectrode with respect to the vacuum level is −4.44 eV (Reference:Toshihiro Ohnishi and Tamami Koyama, High Molecular EL Material,Kyoritsu Shuppan, pp. 64-67). Accordingly, the potential energy of thereference electrode used in this example with respect to the vacuumlevel could be calculated to be −4.44−0.50=−4.94 [eV].

Measurement Example 1 2,5-diphenyl-1,3,4-oxadiazole

First, in this measurement example, calculation of the ionizationpotential and the electron affinity by the CV measurement will bedescribed in detail.

Further, FIG. 13 shows CV measurement results of the oxidationcharacteristics of 2,5-diphenyl-1,3,4-oxadiazole. The measurement of theoxidation characteristics was performed by scanning the potential of theworking electrode with respect to the reference electrode from −0.14 Vto 1.50 V, and then from 1.50 V to −0.14 V.

As shown in FIG. 13, in the measurement of the oxidationcharacteristics, a peak which indicates oxidation does not appear untilabout at least 1.20 V. Further, even if there was a peak which indicatesoxidation at a voltage greater than or equal to 1.20 V, the peak couldnot be observed due to the influence of flow of a large amount ofcurrent. That is, from this data, it is found that the oxidationpotential of 2,5-diphenyl-1,3,4-oxadiazole is greater than or equal toat least 1.20 V. Here, the potential energy of the reference electrodeused in this example with respect to the vacuum level is −4.94 [eV] asdescribed above. Therefore, the oxidation potential of 1.20 V in the CVmeasurement is converted into the HOMO level to give −(−4.94−1.20)=−6.14eV. Accordingly, it was found that the ionization potential of2,5-diphenyl-1,3,4-oxadiazole is greater than or equal to at least 6.14eV.

FIG. 14 shows CV measurement results of the reduction characteristics of2,5-diphenyl-1,3,4-oxadiazole. Note that the measurement of thereduction characteristics was conducted by scanning the potential of theworking electrode with respect to the reference electrode from −1.45 Vto −2.70 V, and then from −2.70 V to −1.45 V.

As shown in FIG. 14, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.51V.Further, the oxidation peak potential E_(pa) was −2.39V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.45 V. This shows that2,5-diphenyl-1,3,4-oxadiazole is reduced by an electric energy of −2.45[V vs. Ag/Ag⁺], and this energy corresponds to the LUMO level. Here, thepotential energy of the reference electrode used in this example withrespect to the vacuum level is −4.94 [eV] as described above. Therefore,the LUMO level of 2,5-diphenyl-1,3,4-oxadiazole was found to be−4.94−(−2.45)=−2.49 [eV]. Accordingly, the electron affinity of2,5-diphenyl-1,3,4-oxadiazole was calculated to be 2.49 eV.

Measurement Example 2 2-phenylbenzoxazole

Further, FIG. 15 shows CV measurement results of the oxidationcharacteristics of 2-phenylbenzoxazole. The measurement of the oxidationcharacteristics was performed by scanning the potential of the workingelectrode with respect to the reference electrode from −0.18 V to 1.50V, and then from 1.50 V to −0.18 V.

As shown in FIG. 15, in the measurement of the oxidationcharacteristics, a peak which indicates oxidation does not appear untilabout at least 1.20 V. Further, even if there were a peak whichindicates oxidation at a voltage greater than or equal to 1.20 V, thepeak could not be observed due to the influence of flow of a largeamount of current. That is, from this data, it is found that theoxidation potential of 2-phenylbenzoxazole is greater than or equal toat least 1.20 V. Here, the potential energy of the reference electrodeused in this example with respect to the vacuum level is −4.94 [eV] asdescribed above. Therefore, the oxidation potential of 1.20 V in the CVmeasurement is converted into the HOMO level to give −(−4.94−1.20)=−6.14eV. Accordingly, it was found that the ionization potential of2-phenylbenzoxazole is greater than or equal to at least 6.14 eV.

FIG. 16 shows CV measurement results of the reduction characteristics of2-phenylbenzoxazole. Note that the measurement of the reductioncharacteristics was conducted by scanning the potential of the workingelectrode with respect to the reference electrode from −1.43 V to −2.64V, and then from −2.64 V to −1.43 V.

As shown in FIG. 16, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.51V.Further, the oxidation peak potential E_(pa) was −2.42V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.47 V. This shows that2-phenylbenzoxazole is reduced by an electric energy of −2.47 [V vs.Ag/Ag⁺], and this energy corresponds to the LUMO level. Here, thepotential energy of the reference electrode used in this example withrespect to the vacuum level is −4.94 [eV] as described above. Therefore,the LUMO level of 2-phenylbenzoxazole was found to be−4.94−(−2.47)=−2.47 [eV]. Accordingly, the electron affmity of2-phenylbenzoxazole was calculated to be 2.47 eV.

Measurement Example 3 phenylcarbazole

Further, FIG. 17 shows CV measurement results of the oxidationcharacteristics of phenylcarbazole. The measurement of the oxidationcharacteristics was performed by scanning the potential of the workingelectrode with respect to the reference electrode from −0.13 V to 1.15V, and then 1.15 V to −0.13 V.

As shown in FIG. 17, in the measurement of the reductioncharacteristics, the oxidation peak potential E_(pa) was 1.02V. Further,the reduction peak potential E_(pc) was 0.86V. Therefore, the half-wavepotential (an intermediate potential between E_(pa) and E_(pc)) can becalculated to be 0.94V. This shows that phenylcarbazole is oxidized byan electric energy of 0.44 [V vs. Ag/Ag⁺], and this energy correspondsto the HOMO level. Here, the potential energy of the reference electrodeused in this example with respect to the vacuum level is −4.94 [eV] asdescribed above. Therefore, the HOMO level of phenylcarbazole was foundto be −4.94−0.94=−5.88 [eV]. Accordingly, the ionization potential ofphenylcarbazole was calculated to be 5.88 [eV].

FIG. 18 shows CV measurement results of the reduction characteristics ofphenylcarbazole. Note that the measurement of the reductioncharacteristics was conducted by scanning the potential of the workingelectrode with respect to the reference electrode from −1.10 V to −3.00V, and then from −3.00 V to −1.10 V.

As shown in FIG. 18, in the measurement of the reductioncharacteristics, a peak which indicates reduction does not appear untilabout at least −2.70 V. Further, even if there were a peak whichindicates reduction at a voltage less than or equal to −2.70 V, the peakcould not be observed due to the influence of flow of a large amount ofcurrent. That is, from this data, it is found that the reductionpotential of phenylcarbazole is less than or equal to at least −2.70 V.Here, the potential energy of the reference electrode used in thisexample with respect to the vacuum level is −4.94 [eV] as describedabove. Therefore, the reduction potential of −2.70 V in the CVmeasurement is converted into the LUMO level to give −4.94−(−2.70)=−2.24eV. Accordingly, it was found that the electron affinity ofphenylcarbazole was less than or equal to at least 2.24 eV.

Measurement Example 4 triphenylamine

FIG. 19 shows CV measurement results of the oxidation characteristics oftriphenylamine. The measurement of the oxidation characteristics wasperformed by scanning the potential of the working electrode withrespect to the reference electrode from 0.01 V to 0.73 V, and then 0.73V to 0.01 V.

As shown in FIG. 19, in the measurement of the oxidationcharacteristics, the oxidation peak potential E_(pa) was 0.67 V.Further, the reduction peak potential E_(pc) was 0.50 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated to be 0.59V. This shows that triphenylamine isoxidized by an electric energy of 0.44 [V vs. Ag/Ag⁺], and this energycorresponds to the HOMO level. Here, the potential energy of thereference electrode used in this example with respect to the vacuumlevel is −4.94 [eV] as described above. Therefore, the HOMO level oftriphenylamine was found to be −4.94−0.59=−5.53 [eV]. Accordingly, theionization potential of triphenylamine was calculated to be 5.53 [eV].

FIG. 20 shows CV measurement results of the reduction characteristics oftriphenylamine. Note that the measurement of the reductioncharacteristics was conducted by scanning the potential of the workingelectrode with respect to the reference electrode from −1.08 V to −3.00V, and then from −3.00 V to −1.08 V.

As shown in FIG. 20, in the measurement of the reductioncharacteristics, a peak which indicates reduction does not appear untilabout at least −2.70 V. Further, even if there were a peak whichindicates reduction at a voltage less than or equal to −2.70 V, the peakcould not be observed due to the influence of flow of a large amount ofcurrent. That is, from this data, it is found that the reductionpotential of triphenylamine is less than or equal to at least −2.70 V.Here, the potential energy of the reference electrode used in thisexample with respect to the vacuum level is −4.94 [eV] as describedabove. Therefore, the reduction potential of −2.70 V in the CVmeasurement is converted into the LUMO level to give −4.94−(−2.70)=−2.24eV. Accordingly, it was found that the electron affinity oftriphenylamine was less than or equal to at least 2.24 eV.

The electron affinity and the ionization potential of2,5-diphenyl-1,3,4-oxadiazole, 2-phenylbenzoxazole,9-phenyl-9H-carbazole, and triphenylamine, which were calculated in theabove measurements, are shown in Table 1.

TABLE 1 Ionization Electron affinity potential Name [eV] [eV] General2,5-diphenyl-1,3,4-oxadiazole 2.49 ≧6.14 formula 2-phenylbenzoxazole2.48 ≧6.14 (G2A) General 9-phenyl-9H-carbazole ≦2.24 5.88 formulatriphenylamine ≦2.24 5.53 (G2B)

As apparent from Table 1, 2,5-diphenyl-1,3,4-oxadiazole and2-phenylbenzoxazole have higher electron affinity and higher ionizationpotential than 9-phenyl-9H-carbazole and triphenylamine.

Further, the electron affinity of 2,5-diphenyl-1,3,4-oxadiazole and2-phenylbenzoxazole is greater than or equal to 2.4 eV and less than orequal to 3.5 eV, and the ionization potential of 9-phenyl-9H-carbazoleand triphenylamine is greater than or equal to 5.0 eV and less than orequal to 6.0 eV.

Accordingly, as the partial structure a of the organic semiconductormaterial according to an embodiment of the present invention, a4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl group which is a2,5-diphenyl-1,3,4-oxadiazole skeleton, or a 4-(benzoxazol-2-yl) groupwhich is a 2-phenylbenzoxazole skeleton can be preferably used. As thepartial structure b, a 4-(9H-carbazol-9-yl) group which has a9-phenyl-9H-carbazole skeleton, or a 4-(diphenylamino)phenyl group whichis a triphenylamine skeleton can be preferably used.

Example 2

In this example, an organic semiconductor material having theelectron-accepting unit and the hole-accepting unit which are describedin Example 1 will be described.

By combining the partial structure a and the partial structure b of thecompound described in Example 1, four kinds of organic semiconductormaterials were synthesized. Structural formulae of the synthesizedorganic semiconductor materials are shown below.

9-[4′″-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPO11) which is represented by Structural Formula (421) has a4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl group which has a2,5-diphenyl-1,3,4-oxadiazole skeleton as the partial structure a, andhas a 4-(9H-carbazol-9-yl) group which has a 9-phenyl-9H-carbazoleskeleton as the partial structure b.

4-[4″-(5-phenyl-1,3,4,-oxadiazol-2-yl)-[1,1′:2′,1″]terphenyl-2-yl]triphenylamine(Z-DPhAO11) which is represented by Structural Formula (460) has a4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl group which has a2,5-diphenyl-1,3,4-oxadiazole skeleton as the partial structure a, andhas a 4-(diphenylamino)phenyl group which has a triphenylamine skeletonas the partial structure b.

9-[4′″-(benzoxazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPBOx) which is represented by Structural Formula (101) has a4-(benzoxazol-2-yl)group which has a 2-phenylbenzoxazole skeleton as thepartial structure a, and has a 4-(9H-carbazol-9-yl) group which has a9-phenyl-9H-carbazole skeleton as the partial structure b.

4-[4″-(benzoxazol-2-yl)-[1,1′:2′,1″]quaterphenyl-2-yl]triphenylamine(Z-DPhABOx) which is represented by Structural Formula (201) has a4-(benzoxazol-2-yl) group which has a 2-phenylbenzoxazole skeleton asthe partial structure a, and has a 4-(diphenylamino)phenyl group whichhas a triphenylamine skeleton as the partial structure b.

Physical properties of these organic semiconductor materials weremeasured. Specifically, CV measurement and measurement of an absorptionspectrum and an emission spectrum were performed.

The CV measurement was performed under the same conditions as that ofExample 1. An electrochemical analyzer (ALS model 600A or 600C,manufactured by BAS Inc.) was used for the measurement. As a solutionused for the CV measurement, dehydrated dimethylformamide (DMF, productof Sigma-Aldrich Inc., 99.8%, Catalog No. 22705-6) was used as asolvent, and tetra-n-butylammonium perchlorate (n-Bu₄NClO₄, product ofTokyo Chemical Industry Co., Ltd., Catalog No. T0836), which was asupporting electrolyte, was dissolved in the solvent such that theconcentration of tetra-n-butylammonium perchlorate was 100 mmol/L.Further, the measurement object was also dissolved such that theconcentration thereof was 2 mmol/L. Further, as a working electrode, aplatinum electrode (a PTE platinum electrode, manufactured by BAS Inc.)was used. As an auxiliary electrode, a platinum electrode (a VC-3 Ptcounter electrode (5 cm), manufactured by BAS Inc.) was used. As areference electrode, an Ag/Ag⁺ electrode (an RE7 nonaqueous solventreference electrode, manufactured by BAS Inc.) was used. Note that themeasurement was conducted at a room temperature (20° C. to 25° C.). Inaddition, the scan speed at the CV measurement was 0.1 V/sec in all themeasurements.

The measurement of the absorption spectrum and the emission spectrum wasperformed using an ultraviolet-visible spectrophotometer (V-550,manufactured by JASCO Corporation). The solution was put into a quartzcell, and the absorption spectrum from which the absorption spectrummeasured when only toluene was put into the quartz cell was subtractedis shown. Thin film samples were each formed by evaporation on a quartzsubstrate, and the absorption spectrum from which the absorptionspectrum of the quartz substrate was subtracted is shown.

<Z-CzPO11>

The oxidation characteristics of Z-CzPO11 were examined as follows. Thepotential of the working electrode with respect to the referenceelectrode was changed from −0.35 V to 1.01 V, and then changed from 1.01V to −0.35 V. This change in potential was regarded as one cycle, andmeasurement was performed for 100 cycles. Further, the reductioncharacteristics of Z-CzPO11 were examined as follows. The potential ofthe working electrode with respect to the reference electrode waschanged from −1.51 V to −2.50 V, and then changed from −2.50 V to −1.51V. This change in potential was regarded as one cycle, and measurementwas performed for 100 cycles.

FIG. 21 shows the CV measurement result of Z-CzPO11 on the oxidationside, and FIG. 22 shows the CV measurement result of Z-CzPO11 on thereduction side. In each of FIGS. 21 and 22, the horizontal axisindicates a potential (V) of the working electrode with respect to thereference electrode, and the vertical axis indicates a current value (A)flowing between the working electrode and the auxiliary electrode. InFIG. 21, a current indicating oxidation was observed at 1.04 V (vs.Ag/Ag⁺ electrode). In FIG. 22, a current indicating reduction wasobserved at −2.40 V (vs. the Ag/Ag⁺ electrode). Since both oxidation andreduction occurred, it was found that Z-CzPO11 was a material into whichboth electrons and holes can be injected, that is, a bipolar material.

In spite of the fact that 100 cycles of scanning were conductedrepeatedly, a peak position and a peak intensity at the CV curvescarcely changed in the oxidation and the reduction. From the result, itwas found that Z-CzPO11 which is an organic semiconductor material ofthe present invention is extremely stable against repetition of theoxidation and reduction. That is, it was found that Z-CzPO11 iselectrochemically stable.

The ionization potential and the electron affinity of Z-CzPO11 werecalculated from the CV measurement result.

As shown in FIG. 21, in the measurement of the oxidationcharacteristics, the oxidation peak potential E_(pa) was 1.04 V.Further, the reduction peak potential E_(pc) was 0.85 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated to be 0.95V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the HOMO level of Z-CzPO11 was found to be−4.94−0.95=−5.89 [eV]. Accordingly, the ionization potential of Z-CzPO11was calculated to be 5.89 [eV].

As shown in FIG. 22, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.40 V.Further, the oxidation peak potential E_(pa) was −2.30 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.35V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the LUMO level of Z-CzPO11 was found to be−4.94−(−2.35)=−2.49 [eV]. Accordingly, the electron affinity of Z-CzPO11was calculated to be 2.59 [eV].

FIG. 23A shows an absorption spectrum and an emission spectrum ofZ-CzPO11 included in a toluene solution and FIG. 23B shows an absorptionspectrum and an emission spectrum of a thin film of Z-CzPO11. In FIGS.23A and 23B, the horizontal axis indicates a wavelength (nm) and thevertical axis indicates intensity (arbitrary unit). In the case of thetoluene solution, absorption was observed at around 302 nm. In the caseof the toluene solution, the maximum emission wavelength was 392 nm(excitation wavelength: 320 nm). In the case of the thin film,absorption was observed at around 236 nm and 298 nm. In the case of thethin film, the maximum emission wavelength was 407 nm (an excitationwavelength: 321 nm).

An absorption edge was obtained from a Tauc plot assuming directtransition with the use of the absorption spectrum data of the thin filmof Z-CzPO11, and the absorption edge was regarded as an optical energygap. Then, the energy gap was estimated to be 3.64 eV. Accordingly, itwas found that Z-CzPO11 has a large optical energy gap.

<Z-DPhAO11>

The oxidation characteristic of Z-DPhAO11 was examined as follows. Thepotential of the working electrode with respect to the referenceelectrode was changed from −0.31 V to 0.75 V, and then changed from 0.75V to −0.31 V. This change in potential was regarded as one cycle, andmeasurement was performed for 100 cycles. Further, the reductioncharacteristics of Z-DPhAO11 were examined as follows. The potential ofthe working electrode with respect to the reference electrode waschanged from −1.36 V to −2.50 V, and then changed from −2.50 V to −1.36V. This change in potential was regarded as one cycle, and measurementwas performed for 100 cycles.

FIG. 24 shows the CV measurement result of Z-DPhAO11 on the oxidationside, and FIG. 25 shows the CV measurement result of Z-DPhAO11 on thereduction side. In each of FIGS. 24 and 25, the horizontal axisindicates a potential (V) of the working electrode with respect to thereference electrode, and the vertical axis indicates a current value (A)flowing between the working electrode and the auxiliary electrode. InFIG. 24, a current indicating reduction was observed at around 0.65 V(vs. Ag/Ag⁺ electrode). In FIG. 25, a current indicating reduction wasobserved at around −2.43 V (vs. the Ag/Ag⁺ electrode). Since oxidationand reduction occurred, it was found that Z-DPhAO11 was a material intowhich electrons and holes can be injected, that is, a bipolar material.

In spite of the fact that 100 cycles of scanning were conductedrepeatedly, a peak position at the CV curve scarcely changed in theoxidation and the reduction. From the result, it was found thatZ-DPhAO11 which is an organic semiconductor material of the presentinvention is extremely stable against repetition of the oxidation andthe reduction. That is, it was found that Z-DPhAO11 is electrochemicallystable.

The ionization potential and the electron affinity of Z-DPhAO11 werecalculated from the CV measurement result.

As shown in FIG. 24, in the measurement of the oxidationcharacteristics, the oxidation peak potential E_(pa) was 0.65 V.Further, the reduction peak potential E_(pc) was 0.51 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated to be 0.58V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the HOMO level of Z-DPhAO11 was found to be−4.94−0.58=−5.52 [eV]. Accordingly, the ionization potential ofZ-DPhAO11was calculated to be 5.52 eV.

As shown in FIG. 25, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.43 V.Further, the oxidation peak potential E_(pa) was −2.31 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.37V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the LUMO level of Z-DPhAO11 was found to be−4.94−(−2.37)=−2.57 [eV]. Accordingly, the electron affinity ofZ-DPhAO11 was calculated to be 2.57 [eV].

FIG. 26A shows an absorption spectrum and an emission spectrum ofZ-DPhAO11 included in a toluene solution and FIG. 26B shows anabsorption spectrum and an emission spectrum of a thin film ofZ-DPhAO11. In FIGS. 26A and 26B, the horizontal axis indicates awavelength (nm) and the vertical axis indicates intensity (arbitraryunit). In the case of the toluene solution, absorption was observed ataround 305 nm. In the case of the toluene solution, the maximum emissionwavelength was 446 nm (excitation wavelength: 334 nm). In the case ofthe thin film, absorption was observed at around 309 nm. In the case ofthe thin film, the maximum emission wavelength was 440 nm (excitationwavelength: 322 nm).

An absorption edge was obtained from a Tauc plot assuming directtransition with the use of the absorption spectrum data of the thin filmof Z-DPhAO11, and the absorption edge was regarded as an optical energygap. Then, the energy gap was estimated to be 3.62 eV. Accordingly, itwas found that Z-DPhAO11 has a large optical energy gap.

<Z-CzPBOx>

The oxidation characteristics of Z-CzPBOx were examined as follows. Thepotential of the working electrode with respect to the referenceelectrode was changed from −0.16 V to 1.10 V, and then changed from−1.10 V to −0.16 V. This change in potential was regarded as one cycle,and measurement was performed for 100 cycles. Further, the reductioncharacteristics of Z-CzPBOx were examined as follows. The potential ofthe working electrode with respect to the reference electrode waschanged from −1.24 V to −2.55 V, and then changed from −2.55 V to −1.24V. This change in potential was regarded as one cycle, and measurementwas performed for 100 cycles.

FIG. 27 shows the CV measurement result of Z-CzPBOx on the oxidationside, and FIG. 28 shows the CV measurement result of Z-CzPBOx on thereduction side. In each of FIGS. 27 and 28, the horizontal axisindicates a potential (V) of the working electrode with respect to thereference electrode, and the vertical axis indicates a current value (A)flowing between the working electrode and the auxiliary electrode. InFIG. 27, a current indicating reduction was observed at around 0.98 V(vs. Ag/Ag⁺ electrode). In FIG. 28, a current indicating reduction wasobserved at around −2.41 V (vs. the Ag/Ag⁺ electrode). Since bothoxidation and reduction occurred, it was found that Z-CzPBOx was amaterial into which both electrons and holes can be injected, that is, abipolar material.

In spite of the fact that 100 cycles of scanning were conductedrepeatedly, a peak position and a peak intensity at the CV curvescarcely changed in the oxidation and the reduction. From the result, itwas found that Z-CzPBOx which is an organic semiconductor material ofthe present invention is extremely stable against repetition of theoxidation and the reduction. That is, it was found that Z-CzPBOx iselectrochemically stable.

The ionization potential and the electron affinity of Z-CzPBOx werecalculated from the CV measurement result.

As shown in FIG. 27, in the measurement of the oxidationcharacteristics, the oxidation peak potential E_(pa) was 0.98 V.Further, the reduction peak potential E_(pc) was 0.85 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated to be 0.92V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the HOMO level of Z-CzPBOx was found to be−4.94−0.92=−5.86 [eV]. Accordingly, the ionization potential of Z-CzPBOxwas calculated to be 5.86 [eV].

As shown in FIG. 28, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.41 V.Further, the oxidation peak potential E_(pa) was −2.28 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.35V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the LUMO level of Z-CzPBOx was found to be−4.94−(−2.35)=−2.60 [eV]. Accordingly, the electron affinity of Z-CzPBOxwas calculated to be 2.60 [eV].

FIG. 29A shows an absorption spectrum and an emission spectrum ofZ-CzPBOx included in a toluene solution and FIG. 29B shows an absorptionspectrum and an emission spectrum of a thin film of Z-CzPBOx. In FIGS.29A and 29B, the horizontal axis indicates a wavelength (nm) and thevertical axis indicates intensity (arbitrary unit). In the case of thetoluene solution, absorption was observed at around 312 nm. In the caseof the toluene solution, the maximum emission wavelength was 390 nm(excitation wavelength: 324 nm). In the case of the thin film,absorption was observed at around 236 nm, 299 nm, and 317 nm. In thecase of the thin film, the maximum emission wavelength was 410 nm(excitation wavelength: 345 nm).

An absorption edge was obtained from a Tauc plot assuming directtransition with the use of the absorption spectrum data of the thin filmof Z-CzPBOx, and the absorption edge was regarded as an optical energygap. Then, the energy gap was estimated to be 3.46 eV. Accordingly, itwas found that Z-CzPBOx has a large optical energy gap.

<Z-DPhABOx>

The oxidation characteristics of Z-DPhABOx were examined as follows. Thepotential of the working electrode with respect to the referenceelectrode was changed from 0.02 V to 0.80 V, and then changed from 0.80V to 0.02 V. This change in potential was regarded as one cycle, andmeasurement was performed for 100 cycles. Further, the reductioncharacteristics of Z-DPhABOx were examined as follows. The potential ofthe working electrode with respect to the reference electrode waschanged from −132 V to −2.55 V, and then changed from −2.55 V to −1.32V. This change in potential was regarded as one cycle, and measurementwas performed for 100 cycles.

FIG. 30 shows the CV measurement result of Z-DPhABOx on the oxidationside, and FIG. 31 shows the CV measurement result of Z-DPhABOx on thereduction side. In each of FIGS. 30 and 31, the horizontal axisindicates a potential (V) of the working electrode with respect to thereference electrode, and the vertical axis indicates a current value (A)flowing between the working electrode and the auxiliary electrode. InFIG. 30, a current indicating reduction was observed at around 0.63 V(vs. Ag/Ag⁺ electrode). In FIG. 31, a current indicating reduction wasobserved at around −2.18 V (vs. the Ag/Ag⁺ electrode). Since oxidationand reduction occurred, it was found that Z-DPhABOx was a material intowhich electrons and holes can be injected, that is, a bipolar material.

In spite of the fact that 100 cycles of scanning were conductedrepeatedly, a peak position and a peak intensity at the CV curvescarcely changed in the oxidation and the reduction. From the result, itwas found that Z-DPhABOx which is an organic semiconductor material ofthe present invention is extremely stable against repetition of theoxidation and the reduction. That is, it was found that Z-DPhABOx iselectrochemically stable.

The ionization potential and the electron affinity of Z-DPhABOx werecalculated from the CV measurement result.

As shown in FIG. 30, in the measurement of the oxidationcharacteristics, the oxidation peak potential E_(pa) was 0.63 V.Further, the reduction peak potential E_(pc) was 0.51 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pa) andE_(pc)) can be calculated to be 0.57V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the HOMO level of Z-DPhABOx was found to be−4.94−0.57=−5.51 [eV]. Accordingly, the ionization potential ofZ-DPhABOx was calculated to be 5.51 [eV].

As shown in FIG. 31, in the measurement of the reductioncharacteristics, the reduction peak potential E_(pc) was −2.42 V.Further, the oxidation peak potential E_(pa) was −2.29 V. Therefore, thehalf-wave potential (an intermediate potential between E_(pc) andE_(pa)) can be calculated to be −2.36V. Since the same referenceelectrode as that in Example 1 is used in this example, the potentialenergy of the reference electrode with respect to the vacuum level is−4.94 [eV]. Therefore, the LUMO level of Z-DPhABOx was found to be−4.94−(−2.36)=−2.59 [eV]. Accordingly, the electron affinity ofZ-DPhABOx was calculated to be 2.59 eV.

FIG. 32A shows an absorption spectrum and an emission spectrum ofZ-DPhABOx included in a toluene solution and FIG. 32B shows anabsorption spectrum and an emission spectrum of a thin film ofZ-DPhABOx. In FIGS. 32A and 32B, the horizontal axis indicates awavelength (nm) and the vertical axis indicates intensity (arbitraryunit). In the case of the toluene solution, absorption was observed ataround 310 nm. In the case of the toluene solution, the maximum emissionwavelength was 450 nm (excitation wavelength: 319 nm). In the case ofthe thin film, absorption was observed at around 318 nm. In the case ofthe thin film, the maximum emission wavelength was 450 nm (excitationwavelength: 344 nm).

An absorption edge was obtained from a Tauc plot assuming directtransition with the use of the absorption spectrum data of the thin filmof Z-DPhABOx, and the absorption edge was regarded as an optical energygap. Then, the energy gap was estimated to be 3.42 eV. Accordingly, itwas found that Z-DPhABOx has a large optical energy gap.

The electron affinity and the ionization potential of Z-CzPO11,Z-DPhAO11, Z-CzPBOx, Z-DPhABOx, which were calculated in the abovemeasurement results, are shown in Table 2.

TABLE 2 Structural Electron affinity Ionization formula Abbreviated name[eV] potential [eV] (421) Z-CzPO11 2.59 5.89 (460) Z-DPhPA11 2.57 5.52(101) Z-CzPBOx 2.60 5.86 (201) Z-DPhABOx 2.59 5.53

As apparent from Table 2, the ionization potentials of Z-CzPO11 andZ-CzPBOx which have the same partial structure b are substantially thesame and substantially the same as the ionization potential of9-phenyl-9H-carbazole shown in Table 1. Similarly, the ionizationpotentials of Z-DPhAO11 and Z-DPhABOx which have the same partialstructure b are substantially the same and substantially the same as theionization potential of triphenylamine shown in Table 1. In other words,the ionization potential of the hole-accepting unit is substantially thesame as that of the organic semiconductor material.

On the other hand, as to the electron-accepting unit, the electronaffinities of Z-CzPO11, Z-DPhAO11, Z-CzPBOx, and Z-DPhABOx aresubstantially the same and substantially the same as those of2,5-diphenyl-1,3,4-oxadiazole and 2-phenylbenzoxazole shown in Table 1.

From the results, it can be said that in an organic semiconductormaterial according to the present invention, extension of conjugation issuppressed by a quaterphenylene group and interaction between anelectron-accepting unit and a hole-accepting unit in a molecule aresuppressed. Accordingly, it was found that the organic semiconductormaterial according to the present invention maintained part ofproperties of an electron-accepting unit and a hole-accepting unit andwas a bipolar material which can transport both electrons and holes.Further, it is considered that even when an electron-accepting unit withlarge electron affinity and a hole-accepting unit with a smallionization potential are used in a molecule at the same time, an organicsemiconductor material with a large band gap can be obtained.

Example 3

In this example, an example of a light-emitting element to which theorganic semiconductor material described in Example 2 is applied will bedescribed with reference to FIG. 33. Structural formula of materialsused in this example are shown below. The material of which structuralformula has already been shown is omitted.

A method for manufacturing a light-emitting element of this example willbe described below.

(Light-Emitting Element 1)

First, a film of indium tin oxide containing silicon oxide (ITSO) wasformed by a sputtering method over a glass substrate 2101 to form afirst electrode 2102. Note that the thickness was 110 nm and theelectrode area was 2 mm×2 mm.

Next, the substrate provided with the first electrode 2102 was fixed toa substrate holder provided in a vacuum evaporation apparatus such thatthe side on which the first electrode 2102 was formed faced downward.After the pressure in a film formation chamber was lowered toapproximately 10⁻⁴ Pa, a layer 2111 containing a composite material ofan organic compound and an inorganic compound was formed on the firstelectrode 2102 by co-evaporation of4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) and molybdenum(VI)oxide. The thickness of the layer 2111 was set to be 40 nm and theweight ratio of NPB to molybdenum(VI) oxide was controlled to 4:1(=NPB:molybdenum oxide). Note that a co-evaporation method refers to anevaporation method by which evaporation is concurrently conducted from aplurality of evaporation sources in one treatment chamber.

Next, 4-(9H-carbazol-9-yl)-4′-phenyltriphenylamine (YGA1BP) is depositedto have a thickness of 20 nm by an evaporation method using resistanceheating to form a hole-transporting layer 2112 on the layer 2111containing a composite material.

Z-CzPO11 which is represented by Structural Formula (421) andbis(2-phenylpyridinato-N,C^(2′))iridium(III)acetylacetonate(Ir(ppy)₂(acac)) were co-evaporated, whereby a light-emitting layer 2113was formed to a thickness of 40 nm on the hole-transporting layer 2112.Here, the weight ratio of Z-CzPO11 to Ir(ppy)₂(acac) was adjusted so asto be 1:0.06 (═Z-CzPO11:Ir(ppy)₂(acac)).

Subsequently, by an evaporation method using resistance heating,bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III) (BAlq) wasdeposited to a thickness of 10 nm on the light-emitting layer 2113,whereby a first electron-transporting layer 2114A was formed. Moreover,bathophenanthroline (BPhen) was deposited on the firstelectron-transporting layer 2114A so as to have a thickness of 20 nm byan evaporation method using resistance heating, whereby a secondelectron-transporting layer 2114B was formed.

Furthermore, a lithium fluoride film was deposited to a thickness of 1nm on the second electron-transporting layer 2114B, whereby anelectron-injecting layer 2115 was formed.

Lastly, an aluminum film was formed to a thickness of 200 nm on theelectron-injecting layer 2115 by an evaporation method using resistanceheating to form a second electrode 2104. Thus, a light-emitting element1 was manufactured.

(Light-Emitting Element 2)

In a manner similar to that of the light-emitting element 1, with theuse of the same substrate as the light-emitting element 1, alight-emitting element 2 was manufactured using Z-DPhAO11 which isrepresented by Structural Formula (460) instead of Z-CzPO11. That is,Z-DPhAO11 and Ir(ppy)₂(acac) were co-evaporated, whereby thelight-emitting layer 2113 was formed to a thickness of 40 nm over thehole-transporting layer 2112. Here, the weight ratio of Z-DPhAO11 toIr(ppy)₂(acac) was adjusted so as to be 1:0.06(═Z-DPhAO11:Ir(ppy)₂(acac)). The layers other than the light-emittinglayer 2113 were formed in a manner similar to that of the light-emittingelement 1.

The thus obtained light-emitting elements 1 and 2 were sealed in a glovebox under a nitrogen atmosphere without being exposed to atmosphericair. Then, the operating characteristics of these light-emittingelements were measured. The measurement was carried out at a roomtemperature (in the atmosphere kept at 25° C.).

FIG. 34 shows the current density-luminance characteristics of thelight-emitting element 1 and the light-emitting element 2. FIG. 35 showsthe voltage-luminance characteristics. FIG. 36 shows theluminance-current efficiency characteristics. FIG. 34 and FIG. 35 showmeasurement data. Based on the data, the luminance-current efficiencycharacteristics (FIG. 36) were calculated.

In addition, a light emission spectrum at current of 1 mA is shown inFIG. 37. From the result shown in FIG. 37, it can be seen that lightemission of the light-emitting elements 1 and 2 is light emissionderived from Ir(ppy)₂(acac). It can be seen that since an organicsemiconductor material of the present invention has high tripletexcitation energy, by using it as a host material of the light-emittinglayer, light emission from a phosphorescent compound which exhibitsgreen light was obtained efficiently.

The CIE chromaticity coordinates of the light-emitting element 1 at aluminance of 850 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 1 at a luminance of 850 cd/m²were 70 cd/A and 19.5%, respectively; thus, the light-emitting element 1had extremely high emission efficiency. The voltage and the currentdensity at a luminance of 850 cd/m² were 4.4 V and 1.21 mA/cm²,respectively. The power efficiency of the light-emitting element 1 was501 m/W, and the light-emitting element 1 had extremely high powerefficiency. Further, energy conversion efficiency was calculated to be9.9% which was high. Furthermore, it can be seen that from FIG. 36, thelight-emitting element 1 has extremely high current efficiency of 70cd/A at maximum.

The CIE chromaticity coordinates of the light-emitting element 2 at aluminance of 830 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 2 at a luminance of 830 cd/m²were 72 cd/A and 20.1%, respectively; thus, the light-emitting element 2had extremely high emission efficiency. The voltage and the currentdensity at a luminance of 830 cd/m² were 4.6 V and 1.15 mA/cm²,respectively. The power efficiency of the light-emitting element 2 was491 m/W, and the light-emitting element 2 had extremely high powerefficiency. Further, energy conversion efficiency was calculated to be9.8% which was high. Furthermore, it can be seen that from FIG. 36, thelight-emitting element 2 has extremely high current efficiency of 72cd/A at maximum.

As seen from the above, by applying an embodiment of the presentinvention, a light-emitting element having extremely high emissionefficiency can be obtained. Further, a light-emitting element with lowdriving voltage can be obtained. The emission efficiency is extremelyhigh and the driving voltage is reduced; therefore, power consumptioncan be reduced.

Example 4

In this example, an example of a light-emitting element to which anorganic semiconductor material described in Example 2 is applied will bedescribed with reference to FIG. 33. Structural formulae of materialsused in this example are shown below. The material of which structuralformula has already been shown is omitted.

A method for manufacturing a light-emitting element of this example willbe described below.

(Light-Emitting Element 3)

A light-emitting element 3 was manufactured usingtris(8-quinolinolato)aluminum(III) (Alq) instead of BAlq of thelight-emitting element 1 which was used in Example 3. That is, an Alqfilm was deposited to a thickness of 10 nm to form a firstelectron-transporting layer 2114A. Except for the firstelectron-transporting layer 2114A, the light-emitting element 3 wasformed in a manner similar to that of the light-emitting element 1.

The light-emitting element 3 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to atmospheric air.Then, the operating characteristics of the light-emitting element weremeasured. The measurement was carried out at a room temperature (in theatmosphere kept at 25° C.).

FIG. 38 shows the current density-luminance characteristics of thelight-emitting element 3. FIG. 39 shows the voltage-luminancecharacteristics. FIG. 40 shows the luminance-current efficiencycharacteristics. FIG. 38 and FIG. 39 show measurement data. Based on thedata, the luminance-current efficiency characteristics (FIG. 40) werecalculated.

In addition, a light emission spectrum at current of 1 mA is shown inFIG. 41. From the result shown in FIG. 41, it can be seen that lightemission of the light-emitting element 3 is light emission derived fromIr(ppy)₂(acac). It can be seen that since an organic semiconductormaterial of the present invention has high triplet excitation energy, byusing it as a host material of the light-emitting layer, light emissionfrom a phosphorescent compound which exhibits green light was obtainedefficiently.

The CIE chromaticity coordinates of the light-emitting element 3 at aluminance of 1020 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 3 at a luminance of 1020 cd/m²were 69 cd/A and 18.9%, respectively; thus, the light-emitting element 3had extremely high emission efficiency. The voltage and the currentdensity at a luminance of 1020 cd/m² were 4.6 V and 1.48 mA/cm²,respectively. The power efficiency of the light-emitting element 3 was471 m/W, and the light-emitting element 3 had extremely high powerefficiency. Further, energy conversion efficiency was calculated to be9.2% which was high. Furthermore, it can be seen that from FIG. 40, thelight-emitting element 3 has extremely high current efficiency of 69cd/A at maximum.

As seen from the above, by applying an embodiment of the presentinvention, a light-emitting element having extremely high emissionefficiency can be obtained. Further, a light-emitting element with lowdriving voltage can be obtained. The emission efficiency is extremelyhigh and the driving voltage is reduced; therefore, power consumptioncan be reduced.

Example 5

In this example, an example of a light-emitting element to which theorganic semiconductor material described in Example 2 is applied will bedescribed with reference to FIG. 33.

A method for manufacturing a light-emitting element of this example willbe described below.

(Light-Emitting Element 4)

A light-emitting element 4 was manufactured in a manner similar to thatof the light-emitting element 1 except that Z-CzPBOx which isrepresented by Structural Formula (101) was used instead of Z-CzPO11 ofthe light-emitting element 1 which was used in Example 3. That is,Z-CzPBOx and Ir(ppy)₂(acac) were co-evaporated, whereby thelight-emitting layer 2113 was formed to a thickness of 40 nm on thehole-transporting layer 2112. Here, the weight ratio of Z-CzPBOx toIr(ppy)₂(acac) was adjusted so as to be 1:0.06(═Z-CzPBOx:Ir(ppy)₂(acac)). The layers other than the light-emittinglayer 2113 were formed in a manner similar to that of the light-emittingelement 1.

(Light-Emitting Element 5)

With the use of the same substrate as the light-emitting element 4, alight-emitting element 5 was manufactured in a manner similar to that ofthe light-emitting element 4 except that Z-DPhABOx which is representedby Structural Formula (201) was used instead of Z-CzPBOx. That is,Z-DPhABOx and Ir(ppy)₂(acac) were co-evaporated, whereby thelight-emitting layer 2113 was formed to a thickness of 40 nm on thehole-transporting layer 2112. Here, the weight ratio of Z-DPhABOx toIr(ppy)₂(acac) was adjusted so as to be 1:0.06(═Z-DPhABOx:Ir(ppy)₂(acac)). The layers other than the light-emittinglayer 2113 were formed in a manner similar to those of thelight-emitting element 4.

The thus obtained light-emitting elements 4 and 5 were sealed in a glovebox under a nitrogen atmosphere without being exposed to atmosphericair. Then, the operating characteristics of these light-emittingelements were measured. The measurements were carried out at a roomtemperature (in the atmosphere kept at 25° C.).

FIG. 42 shows the current density-luminance characteristics of thelight-emitting element 4 and the light-emitting element 5. FIG. 43 showsthe voltage-luminance characteristics. FIG. 44 shows theluminance-current efficiency characteristics. FIG. 42 and FIG. 43 showmeasurement data. Based on the data, the luminance-current efficiencycharacteristics (FIG. 44) were calculated.

In addition, a light emission spectrum at current of 1 mA is shown inFIG. 45. From the result shown in FIG. 45, it can be seen that lightemission of the light-emitting elements 4 and 5 is light emissionderived from Ir(ppy)₂(acac). It can be seen that since a benzoxazolederivative described in Embodiment 2 has high triplet excitation energy,by using it as a host material of the light-emitting layer, lightemission from a phosphorescent compound which exhibits green light wasobtained efficiently.

The CIE chromaticity coordinates of the light-emitting element 4 at aluminance of 1080 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 4 at a luminance of 1080 cd/m²were 49 cd/A and 13.6%, respectively; thus, the light-emitting element 4had high emission efficiency. The voltage and the current density at aluminance of 1080 cd/m² were 5.8 V and 2.22 mA/cm², respectively. Thepower efficiency of the light-emitting element 4 was 261 m/W, and thelight-emitting element 4 had high power efficiency. Further, energyconversion efficiency was calculated to be 5.3% which was high.Furthermore, it can be seen that from FIG. 44, the light-emittingelement 4 has high current efficiency of 54 cd/A at maximum.

The CIE chromaticity coordinates of the light-emitting element 5 at aluminance of 850 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 5 at a luminance of 850 cd/m²were 37 cd/A and 10.4%, respectively; thus, the light-emitting element 5had high emission efficiency. The voltage and the current density at aluminance of 850 cd/m² were 5.4 V and 2.27 mA/cm², respectively. Thepower efficiency of the light-emitting element 5 was 221 m/W, and thelight-emitting element 5 had high power efficiency. Further, energyconversion efficiency was calculated to be 4.3% which was high.Furthermore, it can be seen that from FIG. 44, the light-emittingelement 5 has high current efficiency of 55 cd/A at maximum.

As seen from the above, by applying an embodiment of the presentinvention, a light-emitting element having extremely high emissionefficiency can be obtained. Further, a light-emitting element with lowdriving voltage can be obtained. The emission efficiency is extremelyhigh and the driving voltage is reduced; therefore, power consumptioncan be reduced.

Example 6

In this example, an example of a light-emitting element to which anorganic semiconductor material described in Example 2 is applied will bedescribed with reference to FIG. 33.

A method for manufacturing a light-emitting element of this example willbe described below.

(Light-Emitting Element 6)

A light-emitting element 6 was manufactured usingtris(8-quinolinolato)aluminum(III) (Alq) instead of BAlq of thelight-emitting element 4 in Example 5. That is, an Alq film wasdeposited to a thickness of 10 nm to form a first electron-transportinglayer 2114A. Except for the first electron-transporting layer 2114A, thelight-emitting element 6 was formed in a manner similar to that of thelight-emitting element 4.

The light-emitting element 6 thus obtained was sealed in a glove boxunder a nitrogen atmosphere without being exposed to atmospheric air.Then, the operating characteristics of the light-emitting element weremeasured. The measurement was carried out at a room temperature (in theatmosphere kept at 25° C.).

FIG. 46 shows the current density-luminance characteristics of thelight-emitting element 6. FIG. 47 shows the voltage-luminancecharacteristics. FIG. 48 shows the luminance-current efficiencycharacteristics. FIG. 46 and FIG. 47 show measurement data. Based on thedata, the luminance-current efficiency characteristics (FIG. 48) werecalculated.

In addition, a light emission spectrum at current of 1 mA is shown inFIG. 49. From the result shown in FIG. 49, it can be seen that lightemission of the light-emitting element 6 is light emission derived fromIr(ppy)₂(acac). It can be seen that since an organic semiconductormaterial of the present invention has high triplet excitation energy, byusing it as a host material of the light-emitting layer, light emissionfrom a phosphorescent compound which exhibits green light was obtainedefficiently.

The CIE chromaticity coordinates of the light-emitting element 6 at aluminance of 1150 cd/m² were x=0.35 and y=0.62, and green light emissionwas exhibited. In addition, the current efficiency and external quantumefficiency of the light-emitting element 6 at a luminance of 1150 cd/m²were 70 cd/A and 19.3%, respectively; thus, the light-emitting element 6had extremely high emission efficiency. The voltage and the currentdensity at a luminance of 1150 cd/m² were 6.2 V and 1.66 mA/cm²,respectively. The power efficiency of the light-emitting element 6 was351 m/W, and the light-emitting element 6 had high power efficiency.Further, energy conversion efficiency was calculated to be 7.0% whichwas high. Furthermore, it can be seen that from FIG. 48, thelight-emitting element 6 has high current efficiency of 70 cd/A atmaximum.

As seen from the above, by applying an embodiment of the presentinvention, a light-emitting element having extremely high emissionefficiency can be obtained. Further, a light-emitting element with lowdriving voltage can be obtained. The emission efficiency is extremelyhigh and the driving voltage is reduced; therefore, power consumptioncan be reduced.

Example 7

In this example, a synthesis method of the organic semiconductormaterial according to an embodiment of the present invention which isdescribed in Example 2 will be described in detail.

Synthesis Example 1 Z-CzPO11

A synthesis method of9-[4′″-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPO11) which is represented by following Structural Formula (421)and which is one of the oxadiazole derivatives described in Embodiment 3will be described.

Step 1: Synthesis of 2-(2′-bromobiphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole(i) Synthesis of 4-iodobenzoylhydrazine

A synthetic scheme of 4-iodobenzoylhydrazine is shown in (A-1).

Into a 200 mL three-neck flask was put 25 g (90 mmol) ofethyl-4-iodobenzoate, 80 mL of ethanol was added thereto, and themixture was stirred for 10 minutes at a room temperature. After thestirring, 20 mL of hydrazine monohydrate was added into the solution,and the mixture was stirred at 80° C. for 5 hours. After the stirring,about 500 mL of water was added into the mixture and the mixture waswashed. After the washing, the mixture was subjected to suctionfiltration, and the solid was collected to give 23 g of a whiteneedle-like solid in a yield of 98%.

(ii) Synthesis of 1-benzoyl-2-(4-iodobenzoyl)hydrazine

A synthetic scheme of 1-benzoyl-2-(4-iodobenzoyl)hydrazine is shown in(A-2).

Into a 300 mL three-neck flask was put 15 g (57 mmol) of4-iodobenzoylhydrazine, 15 mL of N-methyl-2-pyrrolidone (NMP) was addedthereto, and the mixture was stirred for 10 minutes at a roomtemperature. After the stirring, 50 mL of a mixed solution of 5 mL ofN-methyl-2-pyrrolidone and 7.9 mL (69 mmol) of benzoyl chloride wasdripped into the solution through a dropping funnel, and the solutionwas stirred at a room temperature for 18 hours. After the stirring,water was added into the solution, and a solid was precipitated. Theprecipitated solid was collected by suction filtration. The collectedsolid was added into about 500 mL of a saturated aqueous solution ofsodium hydrogen carbonate, stirred, and washed. After the washing, themixture was subjected to suction filtration to obtain a solid. Theobtained solid was added into about 500 mL of water, stirred, andwashed. After the washing, the mixture was subjected to suctionfiltration to obtain a solid. The obtained solid was washed withmethanol to give 20 g of a powdery white solid in a yield of 97%.

(iii) Synthesis of 2-(4-iodophenyl)-5-phenyl-1,3,4-oxadiazole

A synthetic scheme of 2-(4-iodophenyl)-5-phenyl-1,3,4-oxadiazole isshown in (A-3).

Into a 300 mL three-neck flask was put 15 g (41 mmol) of1-benzoyl-2-(4-iodobenzoyl)hydrazine, 100 mL of phosphoryl chloride wasadded thereto. The mixture was stirred at 100° C. for 5 hours under anitrogen stream. After the stirring, phosphoryl chloride in the solutionwas distilled off to give a solid. The obtained solid was washed withwater, and then washed with a saturated aqueous solution of sodiumhydrogen carbonate. The obtained solid was washed with methanol to give9.0 g of a powdery white solid in a yield of 63%.

(vi) Synthesis of 2-(2′-bromophenyl-4-yl)-5-phenyl-1,3,4-oxadiazole

A synthetic scheme of 2-(2′-bromophenyl-4-yl)-5-phenyl-1,3,4-oxadiazoleis shown in (A-4).

Into a 100 mL three-neck flask were put 5.0 g (14 mmol) of2-(4-iodophenyl)-5-phenyl-1,3,4-oxadiazole, 2.9 g (14 mmol) of2-bromophenyl boronic acid, 0.032 g (0.14 mmol) of palladium(II)acetate, and 0.30 g (1.0 mmol) of tri(o-tolyl)phosphine. 40 mL of1,2-dimethoxyethane(DME) and 15 mL of a 2M aqueous solution of potassiumcarbonate were added into the mixture. After this mixture was degassedunder low pressure, the atmosphere in the flask was substituted bynitrogen. This mixture was stirred at 90° C. for 5 hours. After thereaction, toluene was added into the mixture, the mixture was separatedinto an aqueous layer and an organic layer, and the organic layer waswashed with a saturated aqueous solution of sodium carbonate and brinein this order. After the washing, magnesium sulfate was added into theorganic layer to dry the organic layer.

After the drying, this mixture was subjected to suction filtration togive a filtrate. The obtained filtrate was subjected to suctionfiltration through Celite (manufactured by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855) to give a filtrate. Thecompound obtained by concentrating the obtained filtrate was purified bysilica gel column chromatography. The column chromatography wasperformed first using toluene as a developing solvent and then using amixed solvent of toluene and ethyl acetate (toluene:ethyl acetate=10:1)as a developing solvent. The obtained fraction was concentrated,methanol was added thereto, and irradiation with ultrasonic waves wasperformed, so that a solid was precipitated. The precipitated solid wascollected by suction filtration. The collected solid was recrystallizedwith a mixed solvent of ethanol and hexane to give 3.1 g of a powderywhite solid in a yield of 58%.

Step 2: Synthesis of 4′-(9H-carbazol-9-yl)biphenyl-2-boronic acid (i)Synthesis of 9-(2′-bromophenyl-4-yl)-9H-carbazole

A synthetic scheme of 9-(2′-bromophenyl-4-yl)-9H-carbazole is shown in(B-1).

Into a 200 mL three-neck flask were put 5.0 g (17 mmol) of4-(9H-carbazol-9-yl)phenylboronic acid, 9.9 g (35 mmol) of2-bromoiodobenzene, 0.039 g (0.17 mmol) of palladium(II) acetate, and0.37 g (1.2 mmol) of tri(o-tolyl)phosphine. After 30 mL of toluene, 5 mLof ethanol, 15 mL of a 2M aqueous solution of potassium carbonate wereadded into the mixture and this mixture was degassed under low pressure,the atmosphere in the flask was substituted by nitrogen. This mixturewas stirred at 90° C. for 5 hours. After the stirring, toluene was addedinto the mixture and the organic layer was washed with a saturatedaqueous solution of sodium carbonate and brine in this order. After thewashing, magnesium sulfate was added into the organic layer to dry theorganic layer. After the drying, this mixture was subjected to suctionfiltration to give a filtrate. The obtained filtrate was concentrated,and was purified by silica gel column chromatography. The columnchromatography was performed first using hexane as a developing solventand then using a mixed solvent of hexane and ethyl acetate (hexane:ethylacetate=20:1) as a developing solvent. The obtained fraction wasconcentrated and dried to give 6.0 g of colorless oily substance in ayield of 86%.

(ii) Synthesis of 4′-(9H-carbazol-9-yl)biphenyl-2-boronic acid

A synthesis scheme of 4′-(9H-carbazol-9-yl)biphenyl-2-boronic acid isshown in (B-2).

Into 300 mL three-neck flask were put a mixed solution of 6.2 g (16mmol) of 9-(2′-bromophenyl)-9H-carbazole and 100 mL of tetrahydrofuran(THF). After the solution was degassed under low pressure, theatmosphere in the flask was substituted by nitrogen. The solution wasstirred at −78° C. for 20 minutes. After the stirring, 12 mL (19 mmol)of hexane solution of 1.55 mol/L of n-butyllithium was dripped with asyringe, and the solution was stirred at −78° C. for 2 hours. After thestirring, 4.0 mL of trimethyl borate was added and the mixture wasstirred −78° C. for 1 hour, and then was stirred for about 24 hourswhile the temperature of the mixture was being gradually brought back toroom temperature. After the stirring, to this solution was added 50 mLof 1M dilute hydrochloric acid, and the solution was stirred for 30minutes at a room temperature. After the stirring, to this mixture wasadded ethyl acetate, and extraction with ethyl acetate was performed.After the extraction, the extracted solution was combined with theorganic layer and washed with brine. After the washing, magnesiumsulfate was added into the organic layer to dry the organic layer. Afterthe drying, the mixture was subjected to suction filtration to give afiltrate. The obtained filtrate was concentrated and recrystallized witha mixture solvent of chloroform and hexane to give 3.2 g of a powderywhite solid in a yield of 55%.

Step 3: Synthesis of Z-CzPO11

A synthetic scheme of Z-CzPO11 is shown in (E-1).

Into a 100 mL three-neck flask were put 1.0 g (2.7 mmol) of2-(2′-bromobiphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole which wassynthesized in Step 1 of Synthesis Example 1, 1.0 g (2.7 mmol) of4′-(9H-carbazol-9-yl)biphenyl-2-boronic acid, 0.010 g (0.045 mmol) ofpalladium(II) acetate, and 0.10 g (0.33 mmol) of tri(o-tolyl)phosphinewhich were synthesized in Step 2 of Synthesis Example 1. Into thesolution were added 15 mL of 1,2-dimethoxyethane (DME) and 10 mL of a 2Maqueous solution of potassium carbonate. After the mixture was degassedunder low pressure, the atmosphere in the flask was substituted bynitrogen. This mixture was stirred at 90° C. for 10 hours. After thestirring, chloroform was added into the mixture, the mixture wasseparated into an aqueous layer and an organic layer, and the organiclayer was washed with a saturated aqueous solution of sodium carbonateand brine in this order. After the washing, magnesium sulfate was addedinto the organic layer to dry the organic layer. After the drying, thismixture was subjected to suction filtration to give a filtrate. Theobtained filtrate was subjected to suction filtration through Celite(manufactured by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855) to give a filtrate. The compound obtained by concentratingthe obtained filtrate was purified by silica gel column chromatography.The column chromatography was performed first using toluene as adeveloping solvent and then using a mixed solvent of toluene and ethylacetate (toluene:ethyl acetate=10:1) as a developing solvent. A solidwhich was obtained by concentrating the obtained fraction was dissolvedin chloroform and purified by high performance liquid chromatography(HPLC). The chromatography was performed using chloroform as adeveloping solvent. The solid which was obtained by concentrating theobtained fraction was recrystallized with a mixed solvent of chloroformand methanol to give 0.30 g of a powdery white solid in a yield of 18%.

The obtained compound was analyzed by nuclear magnetic resonance (NMR)measurement, whereby it was confirmed that the compound was9-[4′″-(5-phenyl-1,3,4-oxadiazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPO11).

Hereinafter, the ¹H NMR data is shown.

¹H NMR(CDCl₃, 300 MHz): δ=6.79 (d, J=8.3 Hz, 2H), 6.88 (d, J=8.3 Hz,2H), 7.22 (d, J=8.3 Hz, 2H), 7.25-7.33 (m, 4H), 7.39-7.62 (m, 13H), 7.84(d, J=8.3 Hz, 2H), 8.09-8.18 (m, 4H)

Further, ¹H NMR charts are shown in FIGS. 50A and 50B. Note that FIG.50B shows an enlarged chart showing the range of 6.5 ppm to 8.5 ppm inFIG. 50A.

Thermogravimetry-differential thermal analysis (TG-DTA) was performed onthe obtained Z-CzPO11. A thermogravimetric-differential thermal analyzer(TG/DTA-320, manufactured by Seiko Instruments Inc.) was used for themeasurement, and it was found that the temperature at which the weightis 95% with respect to the weight at the onset of measurement underatmospheric pressure (hereinafter, this temperature is referred to as“5% weight loss temperature”) was 387° C. The glass transitiontemperature of Z-CzPO11, which was measured using a differentialscanning calorimetry (Pyris 1 DSC, manufactured by Perkin Elmer Co.,Ltd.), was 119° C. From these results, it was found that Z-CzPO11 was amaterial having favorable heat resistance.

Synthesis Example 2 Z-DPhAO11

A synthesis method of4-[4″-(5-phenyl-1,3,4,-oxadiazol-2-yl)-[1,1′:2′,1″]terphenyl-2-yl]triphenylamine(Z-DPhAO11) represented by Structural Formula (460) which is one of theoxadiazole derivatives described in Embodiment 3 will be described.

Step 1: Synthesis of 4′-(N,N-diphenylamino)biphenyl-2-boronic acid (i)Synthesis of 4-(diphenylamino)phenylboronic acid

A synthetic scheme of 4-(diphenylamino)phenylboronic acid is shown in(C-1).

A solution in which 10 g (31 mmol) of 4-bromotriphenylamine is dissolvedin 200 mL of tetrahydrofuran (THF) was put into a 500 mL three-neckflask and stirred. After the solution was degassed under low pressure,the atmosphere in the flask was substituted by nitrogen. The solutionwas stirred at −78° C. for 20 minutes. After the stirring, 24 mL (37mmol) of hexane solution of 1.55 mol/L of n-butyllithium was drippedwith a syringe, and the solution was stirred at −78° C. for 2 hours.After the stirring, 8.0 mL (72 mmol) of trimethyl borate was added andthe mixture was stirred −78° C. for 1 hour, and then was stirred forabout 24 hours while the temperature of the mixture was being graduallybrought back to room temperature. After the stirring, to this solutionwas added 50 mL of 1M dilute hydrochloric acid, and the solution wasstirred for 30 minutes at a room temperature. After the stirring, tothis mixture was added ethyl acetate, and extraction with ethyl acetatewas performed. After the extraction, the extracted solution was combinedwith the organic layer and washed with brine. After the washing,magnesium sulfate was added into the organic layer to dry the organiclayer. After the drying, this mixture was subjected to suctionfiltration to give a filtrate. The obtained filtrate was concentratedand recrystallized with a mixture solvent of toluene and hexane to give5.5 g of a powdery white solid in a yield of 62%.

(ii) Synthesis of 4-(2′-bromophenyl)triphenylamine

A synthetic scheme of 4-(2′-bromophenyl)triphenylamine is shown in(C-2).

Into a 200 mL three-neck flask were put 5.5 g (19 mmol) of4-(diphenylamino)phenylboronic acid, 11 g (38 mmol) of2-bromoiodobenzene, 0.043 g (0.19 mmol) of palladium(II) acetate, and0.41 g (1.3 mmol) of tri(o-tolyl)phosphine. Into the mixture were added30 mL of toluene, 5 mL of ethanol, and 15 mL of a 2M aqueous solution ofpotassium carbonate. After the mixture was degassed under low pressure,the atmosphere in the flask was substituted by nitrogen. The mixture wasstirred at 90° C. for 5 hours. After the stirring, toluene was addedinto the mixture and the organic layer was washed with a saturatedaqueous solution of sodium carbonate and brine in this order. After thewashing, magnesium sulfate was added into the organic layer to thy theorganic layer. After the drying, the mixture was subjected to suctionfiltration to give a filtrate. The obtained filtrate was concentrated,and purification by silica gel column chromatography was performed. Thecolumn chromatography was performed first using hexane as a developingsolvent and then using a mixed solvent of hexane and ethyl acetate(hexane:ethyl acetate=20:1) as a developing solvent. The obtainedfraction was concentrated and dried to give 4.9 g of colorless oilysubstance in a yield of 65%.

(iii) Synthesis of 4′-(diphenylamino)biphenyl-2-boronic acid

A synthetic scheme of 4′-(diphenylamino)biphenyl-2-boronic acid is shownin (C-3).

Into a 300 mL three-neck flask were put a mixed solution of 4.9 g (12mmol) of 4-(2-bromophenyl)triphenylamine and 100 mL of tetrahydrofuran(THF). After the solution was degassed under low pressure, theatmosphere in the flask was substituted by nitrogen. The solution wasstirred at −78° C. for 20 minutes. After the stirring, 9.5 mL (15 mmol)of hexane solution of 1.55 mol/L of n-butyllithium was dripped with asyringe, and the solution was stirred at −78° C. for 2 hours. After thestirring, 2.8 mL (25 mmol) of trimethyl borate was added to the mixtureand the mixture was stirred at −78° C. for 1 hour, and then was stirredfor about 18 hours while the temperature of the mixture was beinggradually brought back to room temperature. After the stirring, to thissolution was added 50 mL of 1M dilute hydrochloric acid, and thesolution was stirred for 30 minutes at a room temperature. After thestirring, to this mixture was added ethyl acetate, and extraction withethyl acetate was performed. After the extraction, the extractedsolution was combined with the organic layer and washed with brine.After the washing, magnesium sulfate was added into the organic layer todry the organic layer. After the drying, the mixture was subjected tosuction filtration to give a filtrate. The obtained filtrate wasconcentrated and recrystallized with a mixture solvent of toluene andhexane to give 2.4 g of a powdery white solid in a yield of 55%.

Step 2: Synthesis of Z-DPhAO11

A synthetic scheme of Z-DPhAO11 is shown in (E-2).

Into a 100 mL three-neck flask were put 1.0 g (2.7 mmol) of2-(2′-bromobiphenyl-4-yl)-5-phenyl-1,3,4-oxadiazole which wassynthesized in Step 1 of Synthesis Example 1, 0.97 g (2.7 mmol) of4′-(diphenylamino)biphenyl-2-boronic acid which was synthesized in Step1 of Synthesis Example 2, 0.010 g (0.045 mmol) of palladium(II) acetate,and 0.10 g (0.33 mmol) of tri(o-tolyl)phosphine. Into the mixture wereadded 15 mL of 1,2-dimethoxyethane (DME) and 15 mL of a 2M aqueoussolution of potassium carbonate. After the mixture was degassed underlow pressure, the atmosphere in the flask was substituted by nitrogen.This mixture was stirred at 90° C. for 10 hours. After the stirring,toluene was added into the mixture, the mixture was separated into anaqueous layer and an organic layer, and the organic layer was washedwith a saturated aqueous solution of sodium carbonate and brine in thisorder. After the washing, magnesium sulfate was added into the organiclayer to dry the organic layer. After drying, the mixture was subjectedto suction filtration to give a filtrate. The obtained filtrate wassubjected to suction filtration through Celite (manufactured by WakoPure Chemical Industries, Ltd., Catalog No. 531-16855) to give afiltrate. The compound obtained by concentrating the obtained filtratewas purified by silica gel column chromatography. The columnchromatography was performed first using toluene as a developing solventand then using a mixed solvent of toluene and ethyl acetate(toluene:ethyl acetate=20:1) as a developing solvent. A solid which wasobtained by concentrating the obtained fraction was dissolved inchloroform and purified by high performance liquid chromatography(HPLC). The chromatography was performed using chloroform as adeveloping solvent. The solid which was obtained by concentrating theobtained fraction was recrystallized with a mixed solvent of chloroformand methanol to give 0.60 g of a powdery white solid in a yield of 37%.

Sublimation purification of 0.60 g of the obtained white solid wasperformed by a train sublimation method. The sublimation purificationwas performed under a reduced pressure of 7.0 Pa, with a flow rate ofargon at 4 mL/min, at 230° C. for 18 hours. After the sublimationpurification, 0.55 g of an objective compound was obtained in a yield of92%.

The obtained compound was analyzed by nuclear magnetic resonance (NMR)measurement, whereby it was confirmed that the compound was4-[4″-(5-phenyl-1,3,4,-oxadiazol-2-yl)-[1,1′:2′,1″]terphenyl-2-yl]triphenylamine(Z-DPhAO11).

Hereinafter, the ¹H NMR data is shown.

¹H NMR (CDCl₃, 300 MHz): δ=6.44 (d, J=8.8 Hz, 2H), 6.72 (d, J=8.8 Hz,2H), 6.86 (d, J=8.8 Hz, 2H), 6.97-7.56 (m, 21H), 7.79 (d, J=8.3 Hz, 2H),8.09-8.13 (m, 2H)

Further, the ¹H NMR chart is shown in FIGS. 51A and 51B. Note that FIG.51B shows an enlarged chart showing the range of 6.5 ppm to 8.5 ppm inFIG. 51A.

Thermogravimetry-differential thermal analysis (TG-DTA) was performed onthe obtained Z-DPhAO11. The measurement performed using athermogravimetric/differential thermal analyzer (TG/DTA 320,manufactured by Seiko Instruments Inc.) revealed that the 5% weight losstemperature was 395° C. The glass transition temperature of Z-DPhAO11,which was measured using a differential scanning calorimetry (Pyris 1DSC, manufactured by Perkin Elmer Co., Ltd.), was 99° C. From theseresults, it was found that Z-DPhAO11 was a material having favorableheat resistance.

Synthesis Example 3 Z-CzPBOx

A synthesis method of9-[4′″-(benzoxazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPBOx) represented by Structural Formula (101) which is one ofbenzoxazole derivatives described in Embodiment 2 will be described.

Step 1: Synthesis of 2-(2′-bromobiphenyl-4-yl)benzoxazole (i) Synthesisof 4-iodobenzoylchloride

A synthesis scheme of 4-iodobenzoylchloride is shown in (D-1).

Into a 200 mL three-neck flask was put 25 g (0.10 mol) of 4-iodobenzoateand were added 70 mL of thionyl chloride and 3 drops ofN,N-dimethylformamide (DMF). The mixture was stirred under a nitrogengas stream at 80° C. for 3 hours. After the stirring, thionyl chloridein the reaction solution was distilled under a reduced pressure andremoved to give a light-yellow oily substance.

(ii) Synthesis of 4-iodo-N-(2-hydroxyphenyl)benzamide

A synthetic scheme of 4-iodo-N-(2-hydroxyphenyl)benzamide is shown in(D-2).

In a 300 mL three-neck flask were put 10 g (92 mmol) of 2-aminophenoland 7.0 mL of triethylamine and was added 100 mL of tetrahydrofuran(THF). The solution was stirred at 0° C. for 20 minutes. After thestirring, a solution in which 0.10 mol of 4-iodobenzoyl chloride wasdissolved in 100 mL of tetrahydrofuran (THF) was dropped. The solutionwas stirred at 0° C. for 5 hours under a nitrogen stream. After thestirring, the solution was added to about 300 mL of water and an aqueouslayer of the obtained mixture was extracted with ethyl acetate. Afterthe extraction, the extracted solution was combined with the organiclayer and washed with 1 M hydrochloric acid, a saturated aqueoussolution of sodium hydrogen carbonate and brine in this order. After thewashing, magnesium sulfate was added into the organic layer to dry theorganic layer. After the drying, the mixture was subjected to suctionfiltration through Celite (manufactured by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855) to give a filtrate. The solid,which was obtained by condensation of the obtained filtrate, wasrecrystallized with a mixed solvent of ethyl acetate and hexane to give30 g of a powdery white solid in a yield of 97%.

(iii) Synthesis of 2-(4-iodophenyl)benzoxazole

A synthetic scheme of 2-(4-iodophenyl)benzoxazole is shown in (D-3).

Into a 300 mL three-neck flask were put 15 g (44 mmol) of4-iode-N-(2-hydroxyphenyl)benzamide and 24 g (0.14 mol) ofpara-toluenesulfonic acid monohydrate and the atmosphere in the flaskwas substituted by nitrogen. 300 mL of toluene was added to the mixture.The mixture was stirred at 110° C. for 4 hours under a nitrogen gasstream. After the stirring, the reaction mixture was added to about 300mL of water, and then the aqueous layer of the mixture was extractedwith ethyl acetate. After the extraction, the extracted solution wascombined with the organic layer and washed with a saturated aqueoussolution of sodium hydrogen carbonate and brine in this order. After thewashing, magnesium sulfate was added into the organic layer to dry theorganic layer. After the drying, the mixture was subjected to suctionfiltration through Celite (manufactured by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855) to give a filtrate. The solidwhich was obtained by concentrating the obtained filtrate wasrecrystallized with a mixed solvent of ethyl acetate and hexane to give11 g of a powdery white solid in a yield of 75%.

(iv) Synthesis of 2-(2′-bromobiphenyl-4-yl)benzoxazole

A synthetic scheme of 2-(2′-bromobiphenyl-4-yl)benzoxazole is shown in(D-4).

Into a 100 mL three-neck flask were put 7.0 g (22 mmol) of2-(4-iodophenyl)benzoxazole, 4.4 g (22 mmol) of 2-bromophenylboronicacid, 0.049 g (0.22 mmol) of palladium(II) acetate, and 0.46 g (1.5mmol) of tri(o-tolyl)phosphine. Into the mixture were added 60 mL of1,2-dimethoxyethane (DME) and 30 mL of a 2M aqueous solution ofpotassium carbonate. After the mixture was degassed under low pressure,the atmosphere in the flask was substituted by nitrogen. This mixturewas stirred at 90° C. for 10 hours. After the stirring, toluene wasadded into the mixture and the organic layer was washed with a saturatedaqueous solution of sodium carbonate and brine in this order. After thewashing, magnesium sulfate was added into the organic layer to dry theorganic layer. After the drying, the mixture was subjected to suctionfiltration to give a filtrate. The obtained filtrate was subjected tosuction filtration through Celite (manufactured by Wako Pure ChemicalIndustries, Ltd., Catalog No. 531-16855) to give a filtrate. Theobtained filtrate was concentrated, and purification by silica gelcolumn chromatography was performed. The column chromatography wasperformed first using a mixed solvent of chloroform and hexane(chloroform:hexane=1:4) as a developing solvent and then using a mixedsolvent of chlorofoini and hexane (chloroform:hexane=1:1) as adeveloping solvent. An obtained fraction was concentrated to give asolid. The obtained solid was recrystallized with a mixed solvent ofchloroform and hexane to give 2.2 g of a powdery white solid in a yieldof 29%.

Step 2: Synthesis of Z-CzPBOx

A synthesis scheme of Z-CzPBOx is shown in (E-3)

Into a 200 mL three-neck flask were put 2.1 g (5.7 mmol) of2-(2′-bromobiphenyl-4-yl)benzoxazole which was synthesized in Step 1 ofSynthesis Example 3, 2.0 g (5.7 mmol) of4′-(9H-carbazol-9-yl)biphenyl-2-boronic acid which was synthesized inStep 2 of Synthesis Example 1, 0.020 g (0.089 mmol) of palladium(II)acetate, and 0.20 g (0.65 mmol) of tri(o-tolyl)phosphine. Into themixture were added 30 mL of 1,2-dimethoxyethane (DME) and 30 mL of a 2Maqueous solution of potassium carbonate. After the mixture was degassedunder low pressure, the atmosphere in the flask was substituted bynitrogen. The mixture was stirred at 90° C. for 10 hours. After thestirring, chloroform was added into the mixture, and the organic layerwas washed with a saturated aqueous solution of sodium carbonate andbrine in this order. After the washing, magnesium sulfate was added intothe organic layer to dry the organic layer. After the drying, themixture was subjected to suction filtration to give a filtrate. Theobtained filtrate was subjected to suction filtration through Celite(manufactured by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855) to give a filtrate. The obtained filtrate was concentrated,and purification by silica gel column chromatography was performed. Thesilica gel column chromatography was performed by using toluene as adeveloping solvent. A solid which was obtained by concentrating theobtained fraction was dissolved in chloroform and purified by highperformance liquid chromatography (HPLC). The chromatography wasperformed using chloroform as a developing solvent. The solid which wasobtained by concentrating the obtained fraction was recrystallized witha mixed solvent of chloroform and methanol to give 2.6 g of a powderywhite solid in a yield of 77%.

Sublimation purification of 2.6 g of the obtained white solid wasperformed by a train sublimation method. The sublimation purificationwas performed under a reduced pressure of 7.0 Pa, with a flow rate ofargon at 4 mL/min, at 250° C. for 15 hours to give 2.3 g of an objectivecompound in a yield of 88%.

The obtained compound was analyzed by nuclear magnetic resonance (NMR)measurement, whereby it was confirmed that the compound was9-[4′″-(benzoxazol-2-yl)-[1,1′:2′,1″:2″,1′″]quaterphenyl-4-yl)]-9H-carbazole(Z-CzPBOx).

Hereinafter, the ¹H NMR data is shown.

¹H NMR (CDCl₃, 300 MHz): δ=6.78 (d, J=8.3 Hz, 2H), 6.87 (d, J=8.3 Hz,2H), 7.15-7.62 (m, 19H), 7.72-7.77 (m, 1H), 7.95 (d, J=8.3 Hz, 2H), 8.16(d, J=7.8 Hz, 2H)

Further, the ¹H NMR chart is shown in FIGS. 52A and 52B. Note that FIG.52B shows an enlarged chart showing the range of 6.5 ppm to 8.5 ppm inFIG. 52A.

Thermogravimetry-differential thermal analysis (TG-DTA) was performed onthe obtained Z-CzPBOx. The measurement was conducted by using a highvacuum differential type differential thermal balance (manufactured byBruker AXS K.K., TG/DTA 2410SA). When the measurement was carried outunder a nitrogen stream (flow rate: 200 mL/min) under a normal pressureat a temperature rising rate of 10° C./min, it was found, from therelationship between weight and temperature (thermogravimetry), that the5% weight loss temperature was 395.2° C.

In addition, a thermal property of Z-CzPBOx was measured using adifferential scanning calorimeter (DSC, manufactured by PerkinElmer,Inc., Pyris 1). First, a sample was heated from −10° C. up to 350° C. ata temperature rising rate of 40° C./min, and then it was cooled down to−10° C. at 40° C./min. After that, Z-CzPBOx was heated up to 290° C. ata temperature rising rate of 10° C./min, thereby obtaining a DSC chart.The peak showing the glass transition temperature of Z-CzPBOx wasobserved in the DSC chart and it was found that the glass transitiontemperature (Tg) was 110° C. From the result, it was found that Z-CzPBOxhas a high glass transition temperature. Accordingly, it was confirmedthat Z-CzPBOx in this synthesis example has high heat resistance.

Synthesis Example 4 Z-DPhABOx

A synthesis method of4-[4″-(benzoxazol-2-yl)-[1,1′:2′,1″]quaterphenyl-2-yl]triphenylamine(Z-DPhABOx) which is represented by following Structural Formula (201)and which is one of the benzoxazole derivatives described in Embodiment2 will be described.

Step 1: Synthesis of Z-DPhABOx

A synthesis scheme of Z-DPhABOx is shown in (E-4).

Into a 100 mL three-neck flask were put 1.0 g (2.9 mmol) of2-(2′-bromobiphenyl-4-yl)benzoxazole which was synthesized in Step 1 ofSynthesis Example 3, 1.0 g (2.9 mmol) of4′-(diphenylamino)biphenyl-2-boronic acid which was synthesized in Step1 of Synthesis Example 2, 0.010 g (0.045 mmol) of palladium(II) acetate,and 0.10 g (0.33 mmol) of tri(o-tolyl)phosphine. Into the mixture wereadded 15 mL of 1,2-dimethoxyethane (DME) and 15 mL of a 2M aqueoussolution of potassium carbonate. After the mixture was degassed underlow pressure, the atmosphere in the flask was substituted by nitrogen.The mixture was stirred at 90° C. for 10 hours. After the stirring,toluene was added into the mixture, and the organic layer was washedwith brine. After the washing, magnesium sulfate was added into theorganic layer to dry the organic layer. After the drying, the mixturewas subjected to suction filtration to give a filtrate. The obtainedfiltrate was subjected to suction filtration through Celite(manufactured by Wako Pure Chemical Industries, Ltd., Catalog No.531-16855) to give a filtrate. The obtained filtrate was concentrated,and purification by silica gel column chromatography was performed. Thecolumn chromatography was performed first using a mixed solvent oftoluene and hexane (toluene:hexane=1:1) as a developing solvent and thenusing toluene as a developing solvent. The solid which was obtained byconcentrating the obtained fraction was recrystallized with a mixedsolvent of chloroform and methanol to give 1.0 g of a powdery whitesolid in a yield of 61%.

Sublimation purification of 1.0 g of the obtained white solid wasperformed by a train sublimation method. The sublimation purificationwas perfoinied under a reduced pressure of 7.0 Pa, with a flow rate ofargon at 4 mL/min, at 230° C. for 20 hours to give 0.84 g of anobjective compound in a yield of 84%.

The obtained compound was analyzed by nuclear magnetic resonance (NMR)measurement, whereby it was confirmed that the compound is4-[4″-benzoxazol-2-yl)-[1,1′:2′,1″]quaterphenyl-2-yl]triphenylamine(Z-DPhABOx).

Hereinafter, the ¹H NMR data is shown.

¹H NMR(CDCl₃, 300 MHz): δ=6.45 (d, J=8.3 Hz, 2H), 6.71 (d, J=8.3 Hz,2H), 6.85 (d, J=8.3 Hz, 2H), 6.98-7.17 (m, 7H), 7.23-7.57 (m, 14H),7.71-7.75 (m, 1H), 7.92 (d, J=7.8 Hz, 2H)

Further, the ¹H NMR chart is shown in FIGS. 53A and 53B. Note that FIG.53B shows an enlarged chart showing the range of 6.5 ppm to 8.5 ppm inFIG. 53A.

In addition, a thermal property of Z-DPhABOx was measured using adifferential scanning calorimeter (DSC, manufactured by PerkinElmer,Inc., Pyris 1). First, a sample was heated from −10° C. up to 350° C. ata temperature rising rate of 40° C./min, and then it was cooled down to−10° C. at 40° C./min. After that, Z-DPhABOx was heated up to 290° C. ata temperature rising rate of 10° C./min, thereby obtaining a DSC chart.The peak showing the glass transition temperature of Z-DPhABOx wasobserved in the DSC chart and it was found that the glass transitiontemperature (Tg) was 98.4° C. From the result, it was found thatZ-DPhABOx has a high glass transition temperature. Accordingly, it wasconfirmed that Z-DPhABOx in this synthesis example has high heatresistance.

This application is based on Japanese Patent Application serial no.2008-229129 filed with Japan Patent Office on Sep. 5, 2008, the entirecontents of which are hereby incorporated by reference.

1. An organic semiconductor material represented by General Formula(G1):

wherein: E_(A) represents an electron-accepting unit; and H_(A)represents a hole-accepting unit.
 2. The organic semiconductor materialaccording to claim 1, wherein E_(A) represents any one of anitrogen-containing 6-membered aromatic ring, a 1,2-azole group, a1,3-azole group, and a polyazole group.
 3. The organic semiconductormaterial according to claim 1, wherein the H_(A) represents a π-electronrich heteroaromatic substituent or a diarylamino group.
 4. An organicsemiconductor material represented by General Formula (BOX1):

wherein: Ar¹ and Ar² each independently represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms; and R¹ to R⁴ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen.
 5. The organic semiconductor material according to claim 4,wherein Ar¹ and a carbon of α are bonded to each other directly orthrough sulfur, oxygen, or nitrogen.
 6. The organic semiconductormaterial according to claim 4, wherein Ar¹ and Ar² are bonded to eachother directly or through sulfur, oxygen, or nitrogen.
 7. The organicsemiconductor material according to claim 4, wherein the organicsemiconductor material is represented by General Formula (BOX2), and

wherein R¹¹ to R²⁰ each independently represent any of hydrogen, alkylgroup having 1 to 4 carbon atoms, or a substituted or unsubstituted arylgroup having 6 to 13 carbon atoms.
 8. The organic semiconductor materialaccording to claim 7, wherein a carbon of the benzene ring which isbonded to R¹¹ and a carbon of α are directly bonded to each other. 9.The organic semiconductor material according to claim 7, wherein acarbon of the benzene ring which is bonded to R¹⁵ and a carbon of thebenzene ring which is bonded to R²⁰ are directly bonded to each other.10. The organic semiconductor material according to claim 7, wherein R¹to R⁴ each are hydrogen.
 11. The organic semiconductor materialaccording to claim 7, wherein R¹¹ to R²⁰ each are hydrogen.
 12. Anorganic semiconductor material represented by General Formula (OXD1):

wherein Ar¹¹, Ar¹², and Ar¹³ each represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.
 13. The organicsemiconductor material according to claim 12, wherein Ar¹¹ and a carbonof α are bonded to each other directly or through any of oxygen, sulfur,or nitrogen.
 14. The organic semiconductor material according to claim12, wherein Ar¹¹ and Ar¹² are bonded to each other directly or throughany of oxygen, sulfur, or nitrogen.
 15. The organic semiconductormaterial according to claim 12, wherein the organic semiconductormaterial is represented by General Formula (OXD2), and

wherein R³¹ to R⁴⁰ represent any of hydrogen, an alkyl group having 1 to4 carbon atoms, or an unsubstituted aryl group having 6 to 13 carbonatoms.
 16. The organic semiconductor material according to claim 15,wherein a carbon of the benzene ring which is bonded to R³¹ and a carbonof α are directly bonded to form a carbazole ring.
 17. The organicsemiconductor material according to claim 15, wherein a carbon of thebenzene ring which is bonded to R³⁵ and a carbon of the benzene ringwhich is bonded to R⁴⁰ are directly bonded to form a carbazole ring. 18.The organic semiconductor material according to claim 15, wherein Ar¹³represents a substituted or unsubstituted phenyl group or a substitutedor unsubstituted naphthyl group.
 19. The organic semiconductor materialaccording to claim 15, wherein Ar¹³ represents a substituted phenylgroup, an unsubstituted 1-naphthyl group, or an unsubstituted 2-naphthylgroup.
 20. The organic semiconductor material according to claim 15,wherein R³¹ to R⁴⁰ each are hydrogen.
 21. A light-emitting elementcomprising: a pair of electrodes; and an organic semiconductor materialrepresented by General Formula (G1),

wherein: E_(A) represents an electron-accepting unit; and H_(A)represents a hole-accepting unit.
 22. A light-emitting elementcomprising: a pair of electrodes; and an organic semiconductor materialrepresented by General Formula (BOX1),

wherein: Ar¹ and Ar² each independently represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms; and R¹ to R⁴ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen.
 23. A light-emitting element comprising: a pair ofelectrodes; and an organic semiconductor material represented by GeneralFormula (OXD1),

wherein Ar¹¹, Ar¹², and Ar¹³ each represents a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.
 24. An electricdevice having a display portion, the display portion comprising alight-emitting element, wherein the light-emitting element comprises: apair of electrodes; and an organic semiconductor material represented byGeneral Formula (BOX1), and

wherein: Ar¹ and Ar² each independently represent a substituted orunsubstituted aryl group having 6 to 13 carbon atoms; and R¹ to R⁴ eachindependently represent any of hydrogen, an alkyl group having 1 to 4carbon atoms, an unsubstituted aryl group having 6 to 10 carbon atoms,or halogen.
 25. An electric device having a display portion, the displayportion comprising a light-emitting element, wherein the light-emittingelement comprises: a pair of electrodes; and an organic semiconductormaterial represented by General Formula (OXD1), and

wherein Ar¹¹, Ar¹², and Ar¹³ each represents a substituted orunsubstituted aryl group having 6 to 13 carbon atoms.